Rough Idle with AC - SOLVED

[Joey82]

Hi All,
I have a '06 4.6 that has a pretty good shake at stops/idles when the AC is going. The idle is pretty noticeable once the car reaches full operating temperature and at least appears to only happen at idle.

I feel like it's air-related so I cleaned my MAF, put in a new Wix air filter and removed/scrubbed down the throttle body. After putting everything together, I did a full relearn process and even reset the accelerator position. Instant gratification over the next week or so and about a half mpg better (city driving). But it's just this idle that's concerning me. I know on my other truck I could replace the Idle Air Control valve, but pretty sure that's somehow in/attached to the throttle and I wasn't sure how to clean it.

Any suggestions or am I going down the wrong patch with the air route?

 

[Fix4Dirt]

could be the compressor being worn/about to lock as well. sometimes thatll do it.

not sure about iac, dont own a 4g

 

[94Eddie]

Hi All,
I have a '06 4.6 that has a pretty good shake at stops/idles when the AC is going. The idle is pretty noticeable once the car reaches full operating temperature and at least appears to only happen at idle.

I feel like it's air-related so I cleaned my MAF, put in a new Wix air filter and removed/scrubbed down the throttle body. After putting everything together, I did a full relearn process and even reset the accelerator position. Instant gratification over the next week or so and about a half mpg better (city driving). But it's just this idle that's concerning me. I know on my other truck I could replace the Idle Air Control valve, but pretty sure that's somehow in/attached to the throttle and I wasn't sure how to clean it.

Any suggestions or am I going down the wrong patch with the air route?

I would suggest looking at what the long and short term fuel trims are doing. This can tell you is you have a fuel delivery issues or a vacuum leak and pin it down to one or both cylinder banks. You could have a small vacuum leak that effects idle when there is a minimal amount of air entering the engine but not when the throttle opens up and lets more air in. Looking at fuel trims will likely confirm or rule out a vacuum leak and can show if you have a fuel delivery issue. The videos below show how to diagnose issues regarding air-fuel ratio using fuel trim info.

 

[Joey82]

I would suggest looking at what the long and short term fuel trims are doing. This can tell you is you have a fuel delivery issues or a vacuum leak and pin it down to one or both cylinder banks. You could have a small vacuum leak that effects idle when there is a minimal amount of air entering the engine but not when the throttle opens up and lets more air in. Looking at fuel trims will likely confirm or rule out a vacuum leak and can show if you have a fuel delivery issue. The videos below show how to diagnose issues regarding air-fuel ratio using fuel trim info.

These videos are addictive lol - thank you! And they inspired me to dig out my cheap Bluetooth OBD2 adapter. I just got back from my 2nd trip, and like a dummy, didn't record the data.

Right now, it's about a good humid 90+ degree morning. Same weather yesterday so pretty comparable conditions. I go to drop my daughter off, about 10 miles each way, and then come home immediately. From my house, it's mostly stop/start with a few decent stretches getting up to around 45mph. As I get into the city, it's your typical stop/start and tons of speed cameras forcing 25mph alot.

Yesterday: On my way in, I started the car with no AC and launched Torque Pro app on Android (with Ford plugins). I noted both the Short Term Fuel trims to be absolutely all over the place. Positive. Negative. Just all over. The Long Term trims though were pretty consistent with each being off by 0.08. Not sure which was which, but one would be 3.1 while the other was like a 2.3. After drop off, I turned the car off. Like two minutes later, I started her back up, (again, no AC), and drove off.

At this point, everything's fully warmed on the truck. And the short terms, still erratic, seemed to swing less. Or I just started ignoring it. About 15 minutes into the return drive home, I started the AC. Ignored the short term again. But the long term consistently went up on both banks. Maybe like 3.9 and 3.1, (again, that stupid 0.08 difference). The car certainly didn't feel any worse. At a light, I turned on the "Max AC/Recirculate" option and immediately noticed the rough idle. No changes to the sensors though. Turned off the "Max AC/Recirculate" but even at the next light - with the regular AC running - the idle was present. Turned everything off shortly after and no rough idle. Went to get a full tank of gas and headed home.

One thing to point out this entire time: When I stepped on the throttle, even with the weight of a feather, the long term (and I think short term), pretty much stayed at 0. Maybe there was that 0.08 difference again, but I mean I barely had to touch the pedal to bring it in line. After watching those videos, the more air you bring in, the more negligible an intake leak would be but to be that negligible? That's insane. Far cry from wide open throttle.

Fast forward to today. Only difference is a fresh tank of gas, (consistently get BP regular with less than 10% ethanol). This time, idiot me thought he was logging the whole drive but with Torque, you need to specify which sensors are logged in the settings. It's not just the ones you're looking at. I learn. But the point is the short term was really not erratic as much. Like variations and all, but not as all over the place. And the long term? Waaaay closer to zero out the outset. And this time a difference of .07 between the two long term banks. Like 1 and 0.03. Again, any pressure to the throttle pulled the long terms, (and I believe short terms), right to 0 or so. No AC again on the way in. This time I left the car running and about 10 minutes in on the return ride home, put the AC (no Max) on. Long terms immediately went to like 2.1 and 1.4 or so. And the rough idle returned at lights, (this time it was irrelevant whether I put on recirculate). Turned the AC off later and things returned to roughly the same values as when I first started her up.


Long-winded, I know. Sorry. But my conclusion is that the sensors/readings might not be all that accurate. Whether it's the age of the car, the cheap bluetooth scanner I have or slight change in air temperature, both drives felt the same despite what Torque said. And as far as the idle, and I think this is key, it's rhythmic. Like when I'm at a light, it'll "shake shake shake smooth smooth shake shake shake shake smooth" and so on. I tried counting the frequency but it was a rough idle more than no rough idle but still consistent from light to light like that. Could this just be a case of needing a tune-up or aging compressor/pulleys or even tired heating systems, (I need to desperately change the coolant. Not many miles since the last flush, but years-wise, at least 5. New hoses, thermostat, radiator, and cap back then but he fluid's old). The one thing I didn't try is seeing how this plays out on a cold/not operating temperature engine. Like the coolant read as high as 210 and I'm putting it on over halfway through the drive. I'm wondering if my engine fan is spinning and I'm putting an additional load with the AC. Sorry, all over the place with this. Regardless, I'll be doing the coolant flush with another thermostat and changing the plugs after seafoaming the heck out of the thing soon.

 

[94Eddie]

These videos are addictive lol - thank you! And they inspired me to dig out my cheap Bluetooth OBD2 adapter. I just got back from my 2nd trip, and like a dummy, didn't record the data.

Right now, it's about a good humid 90+ degree morning. Same weather yesterday so pretty comparable conditions. I go to drop my daughter off, about 10 miles each way, and then come home immediately. From my house, it's mostly stop/start with a few decent stretches getting up to around 45mph. As I get into the city, it's your typical stop/start and tons of speed cameras forcing 25mph alot.

Yesterday: On my way in, I started the car with no AC and launched Torque Pro app on Android (with Ford plugins). I noted both the Short Term Fuel trims to be absolutely all over the place. Positive. Negative. Just all over. The Long Term trims though were pretty consistent with each being off by 0.08. Not sure which was which, but one would be 3.1 while the other was like a 2.3. After drop off, I turned the car off. Like two minutes later, I started her back up, (again, no AC), and drove off.

At this point, everything's fully warmed on the truck. And the short terms, still erratic, seemed to swing less. Or I just started ignoring it. About 15 minutes into the return drive home, I started the AC. Ignored the short term again. But the long term consistently went up on both banks. Maybe like 3.9 and 3.1, (again, that stupid 0.08 difference). The car certainly didn't feel any worse. At a light, I turned on the "Max AC/Recirculate" option and immediately noticed the rough idle. No changes to the sensors though. Turned off the "Max AC/Recirculate" but even at the next light - with the regular AC running - the idle was present. Turned everything off shortly after and no rough idle. Went to get a full tank of gas and headed home.

One thing to point out this entire time: When I stepped on the throttle, even with the weight of a feather, the long term (and I think short term), pretty much stayed at 0. Maybe there was that 0.08 difference again, but I mean I barely had to touch the pedal to bring it in line. After watching those videos, the more air you bring in, the more negligible an intake leak would be but to be that negligible? That's insane. Far cry from wide open throttle.

Fast forward to today. Only difference is a fresh tank of gas, (consistently get BP regular with less than 10% ethanol). This time, idiot me thought he was logging the whole drive but with Torque, you need to specify which sensors are logged in the settings. It's not just the ones you're looking at. I learn. But the point is the short term was really not erratic as much. Like variations and all, but not as all over the place. And the long term? Waaaay closer to zero out the outset. And this time a difference of .07 between the two long term banks. Like 1 and 0.03. Again, any pressure to the throttle pulled the long terms, (and I believe short terms), right to 0 or so. No AC again on the way in. This time I left the car running and about 10 minutes in on the return ride home, put the AC (no Max) on. Long terms immediately went to like 2.1 and 1.4 or so. And the rough idle returned at lights, (this time it was irrelevant whether I put on recirculate). Turned the AC off later and things returned to roughly the same values as when I first started her up.


Long-winded, I know. Sorry. But my conclusion is that the sensors/readings might not be all that accurate. Whether it's the age of the car, the cheap bluetooth scanner I have or slight change in air temperature, both drives felt the same despite what Torque said. And as far as the idle, and I think this is key, it's rhythmic. Like when I'm at a light, it'll "shake shake shake smooth smooth shake shake shake shake smooth" and so on. I tried counting the frequency but it was a rough idle more than no rough idle but still consistent from light to light like that. Could this just be a case of needing a tune-up or aging compressor/pulleys or even tired heating systems, (I need to desperately change the coolant. Not many miles since the last flush, but years-wise, at least 5. New hoses, thermostat, radiator, and cap back then but he fluid's old). The one thing I didn't try is seeing how this plays out on a cold/not operating temperature engine. Like the coolant read as high as 210 and I'm putting it on over halfway through the drive. I'm wondering if my engine fan is spinning and I'm putting an additional load with the AC. Sorry, all over the place with this. Regardless, I'll be doing the coolant flush with another thermostat and changing the plugs after seafoaming the heck out of the thing soon.

I sounds like your fuel trims are good. The long term trims need to be into the double digits before thinking a problem exists or if a problem exists that needs to be addressed. I find that the trims bounce around more when engine load changes. When the load remains consistent they smooth out and stay constant. Since your problem seems to show up when the AC is creating a load it might be an idle speed issues. The computer tells the engine to increase idle speed when the AC is on and even higher when max AC is on. I had my throttle position sensor (TPS) go bad recently and replaced it with the latest iteration from Ford. I was somewhat surprised that the engine seemed to run smoother, idle better and throttle response was a little more precise and smooth. I wonder if your problem might be that your TPS is going bad and and is off just enough to not set idle air intake properly when the AC is on. Here is a video on TPS replacement and which of the three sensors available that you should use as a replacement.

 

[Joey82]

I sounds like your fuel trims are good. The long term trims need to be into the double digits before thinking a problem exists or if a problem exists that needs to be addressed. I find that the trims bounce around more when engine load changes. When the load remains consistent they smooth out and stay constant. Since your problem seems to show up when the AC is creating a load it might be an idle speed issues. The computer tells the engine to increase idle speed when the AC is on and even higher when max AC is on. I had my throttle position sensor (TPS) go bad recently and replaced it with the latest iteration from Ford. I was somewhat surprised that the engine seemed to run smoother, idle better and throttle response was a little more precise and smooth. I wonder if your problem might be that your TPS is going bad and and is off just enough to not set idle air intake properly when the AC is on. Here is a video on TPS replacement and which of the three sensors available that you should use as a replacement.

Sorry to go MIA! It wasn't for lack of effort though. I took your advice on Friday and ordered a new TPS, (normally I'd test the old one with a multimeter and all that stuff, but the fact it was a redesign and based on your comments...why not?). Well, I went with Amazon who could deliver it by Saturday instead of RockAuto who was about 5 days out. The difference was $8. But wait - while in my cart, the price dropped. So the difference wound up being $2 more. Totally a sign, right? Pull the trigger and get it wrapped up before the weekend's out. I thought.

Fast forward to today, and things hit a snag. The "package" was just a sealed envelope/bag. Basically the padding of a zip loc bag. After opening, the Motorcraft bag was open and missing a screw. Fine. But the TPS rattled. Hmm... There was a review mentioning that and the reviewer saying it still worked. So I proceed. Broke a screw. Had fun getting that out but maybe I didn't heat it well enough. Whatever. I get everything in, cleaned the throttle again, (literally the tiniest black mark on a white shirt after spraying & wiping liberally with the CRC throttle cleaner). Fire the car up and immediately noticed the truck really didn't sound like it was running on all cylinders. Or at all even. The moment I touched the throttle, it'd stall out. I went through all my connections, reconnected the battery, etc. Nothing. Luckily I pulled the codes, (all pointing to the TPS) and noticed Torque said the throttle was at like 633 degrees or something. Crazy! Swapped the old one back in and perfect. Took it for a good drive after recalibrating the throttle position and drove like a dream. Except the idle. That issue still persisted.

I did put the AC on before the truck was a full operating temperature, (I'd say around 160F on the coolant), and noticed the throttle position was around 12 degrees. After driving that way on some country roads and stopping to turn back around, I still had the rough idle but noticed the throttle now at 10.9 on the fully warmed up engine. Turned the AC off and idle throttle was between 6-7 degrees.

Going to try and get my refund from Amazon, but now waiting for RockAuto to hopefully getting a functioning part. How much money I get this resolved when the heat season is all done with? Point is though, i wanted to say "thanks" and hoping to have a positive follow up soon!

 

[94Eddie]

Sorry to go MIA! It wasn't for lack of effort though. I took your advice on Friday and ordered a new TPS, (normally I'd test the old one with a multimeter and all that stuff, but the fact it was a redesign and based on your comments...why not?). Well, I went with Amazon who could deliver it by Saturday instead of RockAuto who was about 5 days out. The difference was $8. But wait - while in my cart, the price dropped. So the difference wound up being $2 more. Totally a sign, right? Pull the trigger and get it wrapped up before the weekend's out. I thought.

Fast forward to today, and things hit a snag. The "package" was just a sealed envelope/bag. Basically the padding of a zip loc bag. After opening, the Motorcraft bag was open and missing a screw. Fine. But the TPS rattled. Hmm... There was a review mentioning that and the reviewer saying it still worked. So I proceed. Broke a screw. Had fun getting that out but maybe I didn't heat it well enough. Whatever. I get everything in, cleaned the throttle again, (literally the tiniest black mark on a white shirt after spraying & wiping liberally with the CRC throttle cleaner). Fire the car up and immediately noticed the truck really didn't sound like it was running on all cylinders. Or at all even. The moment I touched the throttle, it'd stall out. I went through all my connections, reconnected the battery, etc. Nothing. Luckily I pulled the codes, (all pointing to the TPS) and noticed Torque said the throttle was at like 633 degrees or something. Crazy! Swapped the old one back in and perfect. Took it for a good drive after recalibrating the throttle position and drove like a dream. Except the idle. That issue still persisted.

I did put the AC on before the truck was a full operating temperature, (I'd say around 160F on the coolant), and noticed the throttle position was around 12 degrees. After driving that way on some country roads and stopping to turn back around, I still had the rough idle but noticed the throttle now at 10.9 on the fully warmed up engine. Turned the AC off and idle throttle was between 6-7 degrees.

Going to try and get my refund from Amazon, but now waiting for RockAuto to hopefully getting a functioning part. How much money I get this resolved when the heat season is all done with? Point is though, i wanted to say "thanks" and hoping to have a positive follow up soon!

I haven't been impressed with Amazon's shipping recently. I swear they drop kick packages into their trucks. Saturday they delivered a letter sized envelope that was open with nothing in it. The delivery guy had to know it was empty. I ordered my TPS off Amazon and it was supposed to be here the next day. The Mountaineer sat for five days waiting on the part to arrive.

When you said the TPS was rattling I figured it was FUBARed. I don't see how one of these parts can rattle and work properly. They are very accurate in how they adjust the throttle blade. I took careful measure to get the temperature of the bolts to 130 degrees by using a laser thermometer. I hate extracting broken off bolts.

 

[Joey82]

Second MIA and just realizing it's been months since I first posted this. But I wanted to say thanks for the help and if anyone finds themselves in the same predicament, my AC idle is gone!

So I realize this is long-winded, but I took a very indirect route in getting this sorted and kind of happened on it by chance. After finally getting a good TPS, I reset the computer and began racking up some miles in hopes of the truck relearning it's tables. Sadly, when the AC was on at full warm-up, (like a half hour of driving), the rough idle was still there. I don't regret the TPS as I've always suspected it of other things like a lag when flooring the truck, etc. Unfortunately, that's still there too, but driving with the new TPS is more than a placebo effect. It's not "wow" but more of running crap gas and filling up with Shell V-Power or something on the next tank. That sort of thing.

As for the truck, I swapped the factory radiator 6 years ago with a Spectre. At that time, I picked up a new thermostat, radiator cap, (20psi), and serpentine belt, (BANDO 6PK2605). Figuring this AC issue is likely not related to the cooling system but definitely begins to happen when the truck is fully warmed up and the fact the coolant is 6 years old, (very low mileage in that time though), why not flush everything? Well, no matter how much love I show this thing, it just creates a million obstacles. When removing the Thermostat housing for the flush, I broke the inner bolt just underneath the throttle body. I wrestled forever but short of removing the intake plenum and hoping I could extract the thing, I decided on going all MacGyver. Before the "open eared design" that started in like 07 or so, the 06 t-stat housing has two ears that are held in by the two bolts. I took a step drill bit to the t-stat housing to create a recess where the bolt would normally go and, treating the now-broken bolt like a stud, secured it with a 6mm nylon locking nut and washer. Genius!

And I ran a flush. This is where the old truck just keeps testing me. There wasn't really a need to toss any product in there, but if you're changing and flushing the cooling, why not put in a bottle of flush I just happened to have on hand, (the Prestone one)? Emptied, added flush and water, drained, added distilled water, drained, added unopened coolant I didn't need 6 years ago, drained, and filled with new coolant. Good, right? Queue a meme of someone pulling your chair right before you sit down.

Finally - get to the solution man!
I noticed my coolant reservoir just about empty after each drive and a strong coolant smell in the engine. As usual, I couldn't find anything so I could only assume my make-shift solution to the T-stat housing was letting some coolant out and immediately burning it off. Fast forward and I broke down and bought one of those cooling system pressure test kits. I only pumped to 10psi and immediately there was coolant come out. I couldn't see exactly where, but it was behind the fan shroud. I'm betting running 6 years on 20psi again and tossing in a flush killed the Spectre unit. Time for another radiator change - this time going back to Motorcraft and adding the 16psi cap. And unlike 6 years ago, since I have everything out, I pickup a new water pump (Motorcraft), 3 new idler pulleys, (Motorcraft & Gates), new Tensioner (Motorcraft), and new serpentine belt, (Motorcraft JK61032AC). As I'm comparing the new and old parts, I immediately noticed the Bando belt from 6 years ago is maybe an inch bigger than the Motorcraft I just bought. But the new one is still a little stiff from packaging and maybe 6 years, even with low miles, put a little slack in the Bando. After I get everything installed and back together, the idle was immediate. Even without the AC engaged!!! Somewhere between the tensioner and belt, (and maybe idler pulleys), the stock spec is back! I realize this is a long rant and of course, AC season is winding down now, but I just wanted to say thanks again and hopefully this helps someone experiencing the same issues or who is about to change a radiator and contemplating whether or not the "extra" stuff is worth it or not.

 

[johnross]

Second MIA and just realizing it's been months since I first posted this. But I wanted to say thanks for the help and if anyone finds themselves in the same predicament, my AC idle is gone!

So I realize this is long-winded, but I took a very indirect route in getting this sorted and kind of happened on it by chance. After finally getting a good TPS, I reset the computer and began racking up some miles in hopes of the truck relearning it's tables. Sadly, when the AC was on at full warm-up, (like a half hour of driving), the rough idle was still there. I don't regret the TPS as I've always suspected it of other things like a lag when flooring the truck, etc. Unfortunately, that's still there too, but driving with the new TPS is more than a placebo effect. It's not "wow" but more of running crap gas and filling up with Shell V-Power or something on the next tank. That sort of thing.

As for the truck, I swapped the factory radiator 6 years ago with a Spectre. At that time, I picked up a new thermostat, radiator cap, (20psi), and serpentine belt, (BANDO 6PK2605). Figuring this AC issue is likely not related to the cooling system but definitely begins to happen when the truck is fully warmed up and the fact the coolant is 6 years old, (very low mileage in that time though), why not flush everything? Well, no matter how much love I show this thing, it just creates a million obstacles. When removing the Thermostat housing for the flush, I broke the inner bolt just underneath the throttle body. I wrestled forever but short of removing the intake plenum and hoping I could extract the thing, I decided on going all MacGyver. Before the "open eared design" that started in like 07 or so, the 06 t-stat housing has two ears that are held in by the two bolts. I took a step drill bit to the t-stat housing to create a recess where the bolt would normally go and, treating the now-broken bolt like a stud, secured it with a 6mm nylon locking nut and washer. Genius!

And I ran a flush. This is where the old truck just keeps testing me. There wasn't really a need to toss any product in there, but if you're changing and flushing the cooling, why not put in a bottle of flush I just happened to have on hand, (the Prestone one)? Emptied, added flush and water, drained, added distilled water, drained, added unopened coolant I didn't need 6 years ago, drained, and filled with new coolant. Good, right? Queue a meme of someone pulling your chair right before you sit down.

Finally - get to the solution man!
I noticed my coolant reservoir just about empty after each drive and a strong coolant smell in the engine. As usual, I couldn't find anything so I could only assume my make-shift solution to the T-stat housing was letting some coolant out and immediately burning it off. Fast forward and I broke down and bought one of those cooling system pressure test kits. I only pumped to 10psi and immediately there was coolant come out. I couldn't see exactly where, but it was behind the fan shroud. I'm betting running 6 years on 20psi again and tossing in a flush killed the Spectre unit. Time for another radiator change - this time going back to Motorcraft and adding the 16psi cap. And unlike 6 years ago, since I have everything out, I pickup a new water pump (Motorcraft), 3 new idler pulleys, (Motorcraft & Gates), new Tensioner (Motorcraft), and new serpentine belt, (Motorcraft JK61032AC). As I'm comparing the new and old parts, I immediately noticed the Bando belt from 6 years ago is maybe an inch bigger than the Motorcraft I just bought. But the new one is still a little stiff from packaging and maybe 6 years, even with low miles, put a little slack in the Bando. After I get everything installed and back together, the idle was immediate. Even without the AC engaged!!! Somewhere between the tensioner and belt, (and maybe idler pulleys), the stock spec is back! I realize this is a long rant and of course, AC season is winding down now, but I just wanted to say thanks again and hopefully this helps someone experiencing the same issues or who is about to change a radiator and contemplating whether or not the "extra" stuff is worth it or not.

One very important thing to do when changing spark plugs, change the boots as well. They have a tendency to hairline crack, which causes spark loss, which in turn causes all sorts of computer problems. With ours, it felt like transmission problems...Talking to another explorer owner, he had transmission issues, he changed the tranny, but still had the same problems. Told him to change spark plug boots, solved all his issues. Strange how something so minor affects the entire computer system.

 

[Astrobuf]

Hi All,
I have a '06 4.6 that has a pretty good shake at stops/idles when the AC is going. The idle is pretty noticeable once the car reaches full operating temperature and at least appears to only happen at idle.

I feel like it's air-related so I cleaned my MAF, put in a new Wix air filter and removed/scrubbed down the throttle body. After putting everything together, I did a full relearn process and even reset the accelerator position. Instant gratification over the next week or so and about a half mpg better (city driving). But it's just this idle that's concerning me. I know on my other truck I could replace the Idle Air Control valve, but pretty sure that's somehow in/attached to the throttle and I wasn't sure how to clean it.

Any suggestions or am I going down the wrong patch with the air route?

It's a 4.6l 3V? I'd be suspicious that your phasers are fragged. You need more than a vote reader to figure this out. I use an Autel engine analyzer. Watch to see if the phasers return to 0 advance at idle. It's possible one or both are stuck advanced some. Very common problem with this engine at the milage you have. Do you hear chain slap? Tensioners and guided frequently shot too. Most likely you need a timing job. ONLY use Ford parts for this job.

 

[D Hook]

Enjoyed the writing!

 

[Turdle]

It's a 4.6l 3V? I'd be suspicious that your phasers are fragged. You need more than a vote reader to figure this out. I use an Autel engine analyzer. Watch to see if the phasers return to 0 advance at idle. It's possible one or both are stuck advanced some. Very common problem with this engine at the milage you have. Do you hear chain slap? Tensioners and guided frequently shot too. Most likely you need a timing job. ONLY use Ford parts for this job.

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