Low idle, been chasing for years!

[briwayjones]

2000 (Manual trans., OHV)

I have had a low fluctuating idle for years. Sometimes it will idle normal, about 700-750, but a lot if not most of the time it will idle around 500, or even drop lower, 300-400. Every once in a while low enough that it will stall.

I have tried three different IAC valves. Including replacing it with a brand new one. I replaced the TPS with a brand new one. Switched out the MAF sensor. I can't find any vacuum leaks. No CELs. This has spanned two different sets of plugs and wires. The head and lower intake gaskets were replaced in the middle of this. None of it has changed the idle.

I'm pretty much out of ideas now. So far I can't find anything on here more than covering these things.

I need some new ideas.

 

[C420sailor]

Did I read recently about a feature in the 5-speed system where it drops the idle when you clutch in or something? I can’t remember, and I’m not knowledgeable about the manuals...anyone?

 

[briwayjones]

Did I read recently about a feature in the 5-speed system where it drops the idle when you clutch in or something? I can’t remember, and I’m not knowledgeable about the manuals...anyone?

You might referring to how while rolling no matter how slow, they usually won't drop below about 1000rpm until you push in the clutch, instead of dropping to normal idle. Then it drops to normal idle speed after you push in the clutch.

 

[C420sailor]

Ah okay, nvm. Thought it could be a fault in that feature

 

[FijiBill]

IAC/MAF/wires would be the likely suspects.

More (less likely) ideas:

Check that the alternator is putting out 13+ volts at idle. Maybe the voltage regulator or brushes are going out on it.

Also check the ground strap at the back of the engine. That completes the circuit for the spark plugs.

The coil pack isn't hard to switch out. It's not very expensive to replace or you could grab one from a junkyard and return it if it doesn't help.

 

[410Fortune]

your oxygen sensors could also be getting lazy? with high miles they do that

Has the throttle body ever been messed with?
I would have a very good look at my throttle body, all hoses attached?
I would TEST your throttle position sensor, should have 4.8-5v with the key on, and the signal should sweep smoothly (plenty of how to's online for this)

A scanner is a good idea so you can see what the actual engine RPM's are according to the computer

I had a 4.0 OHV that had a very low idle, the fix was actually to drill a tiny hole in the butterfly valve (some of the earlier models actually has this from factory).
Another option is an adjustable IAC plate, they make a plate that goes underneath your IAC (between IAC and intake) allowing a tiny bit of air to bypass the IAC, this is a mustang device used to compensate for a low idle due to performance camshaft. I have used them to correct a low idle before.
Last resort would be to actually bump up the idle using the idle screw on the TB

 

[briwayjones]

IAC/MAF/wires would be the likely suspects.

More (less likely) ideas:

Check that the alternator is putting out 13+ volts at idle. Maybe the voltage regulator or brushes are going out on it.

Also check the ground strap at the back of the engine. That completes the circuit for the spark plugs.

The coil pack isn't hard to switch out. It's not very expensive to replace or you could grab one from a junkyard and return it if it doesn't help.

I actually just put a new alternator on it. Wires could be a culprit though. I had an AC wire that went bad. Where is the ground strap located at the back of the engine?

 

[briwayjones]

your oxygen sensors could also be getting lazy? with high miles they do that

Has the throttle body ever been messed with?
I would have a very good look at my throttle body, all hoses attached?
I would TEST your throttle position sensor, should have 4.8-5v with the key on, and the signal should sweep smoothly (plenty of how to's online for this)

A scanner is a good idea so you can see what the actual engine RPM's are according to the computer

I had a 4.0 OHV that had a very low idle, the fix was actually to drill a tiny hole in the butterfly valve (some of the earlier models actually has this from factory).
Another option is an adjustable IAC plate, they make a plate that goes underneath your IAC (between IAC and intake) allowing a tiny bit of air to bypass the IAC, this is a mustang device used to compensate for a low idle due to performance camshaft. I have used them to correct a low idle before.
Last resort would be to actually bump up the idle using the idle screw on the TB

I'll have to look into this stuff.
I have an aftermarket throttle body on it. I tried putting the OEM back on there and it didn't make a difference. Plus I've had the aftermarket one on there for a long time.
What's the chances of a minor vacuum leak so small that it's difficult to find affecting the idle?

I have adjusted the TB idle screw as a stop gap measure before, but that creates other problems. Since the computer tries to compensate for how it's adjusted it actually prevents the engine from decreasing RPM when coming to a stop. While moving it won't let the RPMs drop below about 1300RPM. So when braking to a stop the clutch has to be pushed in when you reach about 1300RPM and it won't idle down until you come to a complete stop.

Before getting one of these plates that go under the IAC, do you think it would work to test this by shimming up the IAC a bit so it doesn't fit as tight?

 

[FijiBill]

I actually just put a new alternator on it. Wires could be a culprit though. I had an AC wire that went bad. Where is the ground strap located at the back of the engine?

The ground strap is on the back of the head (drivers side) and is connected to the firewall. You said the head had been replaced. Maybe it wasn't reconnected properly.

By wires I meant plug wires. But sounds like you've swapped those.

 

[410Fortune]

vacuum leak usually cause a high idle not a low one

Your aftermarket TB is it a BBK?
Test your TPS for proper reference voltage and a clean sweep (no dead spots), if I remember correctly on the 4.0 the tps is slotted and allows a slight amount of adjustment for idle voltage. It has been 20+ years since I have done this but I seem to recall something about 1.65v at idle?
Maybe somebody else will chime in and help us with my memory issues!! hahahaha

The adjustable IAC plate is cool, basically it just has a small hole that allows some air to bypass the iac, you can control how much air by opening or closing a set screw...
$56 seems a little steep but they go up from there.....
Mustang Idle Air Control (IAC) Adjuster (86-93) EFI V8

ford mustang adjustabl;e iac - Google Search

I was going to say you can try drilling a small hole in the butterfly at the TB, essentially doing the same thing as a IAC bypass.
If you do not like the new hole you could always weld/solder it back closed

When I did this we used a stock throttle body plate so if the hole didn't work we could swap them back out, but for us it actually worked.
The stock throttle bodies actually had a small bypass hole in the early years

 

[AA7KN]

2000 (Manual trans., OHV)

I have had a low fluctuating idle for years. Sometimes it will idle normal, about 700-750, but a lot if not most of the time it will idle around 500, or even drop lower, 300-400. Every once in a while low enough that it will stall.

I have tried three different IAC valves. Including replacing it with a brand new one. I replaced the TPS with a brand new one. Switched out the MAF sensor. I can't find any vacuum leaks. No CELs. This has spanned two different sets of plugs and wires. The head and lower intake gaskets were replaced in the middle of this. None of it has changed the idle.

I'm pretty much out of ideas now. So far I can't find anything on here more than covering these things.

I need some new ideas.

hello, i had the same problem in my 96. i found on the botom of the throttle body there is a hard plastic line that goes over to under the front of the drivers side fender to return gas fumes to and from the tank. it had cracked at both ends. I replaced it with a regular fuel line rubber hose. so now the idle was higher than normal. so..on the front of the throttle bosy, at the point where the throttle cable connects, there is a idle speed adjustment screw, i backed it off a couple turns, now she idles smeeth at about 7 to 900 . if you have now vaccume leaks, try the idle screw, it is small so pull off the intake air hose, and you should see it. hope this helps.

 

[AA7KN]

2000 (Manual trans., OHV)

I have had a low fluctuating idle for years. Sometimes it will idle normal, about 700-750, but a lot if not most of the time it will idle around 500, or even drop lower, 300-400. Every once in a while low enough that it will stall.

I have tried three different IAC valves. Including replacing it with a brand new one. I replaced the TPS with a brand new one. Switched out the MAF sensor. I can't find any vacuum leaks. No CELs. This has spanned two different sets of plugs and wires. The head and lower intake gaskets were replaced in the middle of this. None of it has changed the idle.

I'm pretty much out of ideas now. So far I can't find anything on here more than covering these things.

I need some new ideas.

hello, i had the same problem, my idle was high. I found the hard plastic hose under the throttle body had cracks at both ends, so I replaced the hard line with regulad rubber fuel line and now it idles very low, just like yours does, so i removed the air cleaner large hose off the front of the throttle bodty, and under it where the throttle cable connects is a idle speed screw, i just gave it a couple turns clock wise to increase the idle speed, and it works great. make sure to do this after the car has warmed up and the computer is in closed loop, so the idle will be accurate. hope this helps.

 

[briwayjones]

hello, i had the same problem, my idle was high. I found the hard plastic hose under the throttle body had cracks at both ends, so I replaced the hard line with regulad rubber fuel line and now it idles very low, just like yours does, so i removed the air cleaner large hose off the front of the throttle bodty, and under it where the throttle cable connects is a idle speed screw, i just gave it a couple turns clock wise to increase the idle speed, and it works great. make sure to do this after the car has warmed up and the computer is in closed loop, so the idle will be accurate. hope this helps.

Thanks, I'll have to look at that hose.

I haven't messed with anything more yet. I've been avoiding the cold. Now I have another problem, so I'll have to deal with that first.

I've used the idle screw to increase the idle as a stopgap measure in the past. But the computer tries to compensate and it causes other problems.

 

[donalds]

Use the screw on the back of the iac
Here is a link to the post I made

Shoc remanufactured engine with pre oiler timing guide reliability

I’ve seen it in a few motors. 4.3 GMs are notorious for it. Used to happen to my moms Blazer all the time. If your motor can’t be rev’d out a few times a week it’s not fit for service. I ran my old Mounty to the rev limiter all the time. Had 220k hard miles, 20k oil changes and had zero...

www.explorerforum.com

Thanks for the pic @DILLARD000

 

[briwayjones]

vacuum leak usually cause a high idle not a low one

Your aftermarket TB is it a BBK?
Test your TPS for proper reference voltage and a clean sweep (no dead spots), if I remember correctly on the 4.0 the tps is slotted and allows a slight amount of adjustment for idle voltage. It has been 20+ years since I have done this but I seem to recall something about 1.65v at idle?
Maybe somebody else will chime in and help us with my memory issues!! hahahaha

The adjustable IAC plate is cool, basically it just has a small hole that allows some air to bypass the iac, you can control how much air by opening or closing a set screw...
$56 seems a little steep but they go up from there.....
Mustang Idle Air Control (IAC) Adjuster (86-93) EFI V8

ford mustang adjustabl;e iac - Google Search

I was going to say you can try drilling a small hole in the butterfly at the TB, essentially doing the same thing as a IAC bypass.
If you do not like the new hole you could always weld/solder it back closed

When I did this we used a stock throttle body plate so if the hole didn't work we could swap them back out, but for us it actually worked.
The stock throttle bodies actually had a small bypass hole in the early years

Reviving old threads again. It's not a daily driver and mostly a winter vehicle so I've been kind of tolerating it and avoiding messing with it. Lately it got worse though. I need to get this fixed once and for all though. So the latest update:

The first low idle was just when it was cold outside. Then it started doing it when it was warm too. This went on for a couple years of it doing it while warm too. Lately after the last 6 months or so that changed. The low idle seemed to disappear for the most part, but now it was idling way high and wouldn't idle down at all. For instance, it wouldn't really idle below 1500RPM. It would take a bit to come down to that after stopping. While moving but coasting the RPM wouldn't go below 2000-2500RPM. So even while giving no gas and just coasting the engine would pull at about 2500RPM and it wouldn't slow down. As if I was applying 2500RPM with the pedal. Then after coming to a stop sometimes the RPMs wouldn't come lower than 2000RPM. Usually the lowest they would go is the 1500RPM.

What I had done in the past was change the IAC a couple times. First time was an aftermarket, second time a Motorcraft. Neither made any difference. I had also cleaned both once or twice at one time or another. No difference.

I had read that cleaning the throttle body could make a difference. So this time I cleaned everything. I cleaned the MAF, IAC, and took the throttle body off and cleaned it. It was pretty oily and gunky. After that the high idle seemed to go away. It would go down to normal RPMs and not stay high. But new problem. Now when giving it just a little gas, like feathering it, it would try to stall. When giving it a bunch of gas if you could get past the stalling spot it would run fine at higher RPMs. It seemed like a dead spot. So to me it seemed like the TPS was goofy, which never seemed like a problem before. I replaced it with an aftermarket TPS. It was worse, it would stall as soon at you applied gas and you couldn't even get past it to give more gas and run it at higher RPMs. I noticed the slot that engages the throttle body was in a different position than the factory one. So I replaced it with a new Motorcraft. It's slot was the same as the original, as it should be. It didn't help and does the same thing as the factory one. So now we're up to date.

To answer your old question, the aftermarket throttle body is a BBK. You mentioned testing the voltages on the TPS.

I would TEST your throttle position sensor, should have 4.8-5v with the key on, and the signal should sweep smoothly (plenty of how to's online for this)

So I finally tested the voltages following this guide. While doing it I was having deja vu so I wonder if I did it in the past, it checked out and I forgot. Anyway, everything checked out. Both for the new and original TPS. Nice smooth sweep up to 5v at wide open. So I am kind of out of ideas. With the way the throttle had a dead spot in the beginning after cleaning everything I really thought it was the TPS. Should I try to adjust the IAC screw like @donalds mentioned?

 

[EB4X]

I know people say DON'T MESS WITH FACTORY SET IDLE screw.....I got FED up like you not being able to resolve it and cranked mine up....it's been FINE and resolved issue without creating a new one... passed smog with it like that too.... take NOTE of how many turns you do so for whatever reason you want to return it to "pre adjustment" spot you'll have a reference.

 

[briwayjones]

I know people say DON'T MESS WITH FACTORY SET IDLE screw.....I got FED up like you not being able to resolve it and cranked mine up....it's been FINE and resolved issue without creating a new one... passed smog with it like that too.... take NOTE of how many turns you do so for whatever reason you want to return it to "pre adjustment" spot you'll have a reference.

The idle seems to no longer be a problem. It's the stalling when throttle is applied now. But in the past I adjusted the idle screw as a stop gap measure. But it screws with the computer when you do that. The computer tries to compensate for the adjusted idle. When coasting the computer won't allow it to idle down and not let the engine slow down past about 1200RPM or higher depending on how much you adjust it. It's probably more noticeable in a manual than automatic Explorer.

 

[briwayjones]

I should give an update. The problem seems to be fixed now.
Recap: I did a cleaning of everything. The idle seemed better, but then I had that dead spot where the engine would stall or try to stall when first applying gas. I changed the TPS with a new factory one and it didn't make a difference. The final piece of the puzzle was the MAF sensor was bad. When I took it off to clean it, the plastic housing over the sensor itself broke off. It was just plastic so I just glued it back on. But that's when the problem started. I replaced it and now everything runs good and normal. Probably for the first time in about 6 years.

 

[Turdle]

Good to hear from you Brian