2003 Explorer Rough Idle

[Cashcrazy]

Unhooked battery and replaced PCV valve. PCV hose was in good shape. Still a crummy idle. Any more ideas?

 

[Cashcrazy]

I think it might be time to find a fog machine and give it the smoke test. Has anyone had success with this?

 

[plasticseng]

Fuel trim data will diagnose a vacuum leak.

Here is a video on using a cigar as a smoke machine:




Is it missing? Idling fast? Idling slow? Idle speed varying?

 

[Cashcrazy]

I ran across some fuel trim info and have to research it more. Thanks for the video. Much cheaper than buying a dog machine.

 

[Fordman999]

Is your IAC not leaking air? Could be the IAC going bad. Also make sure your plugs are in the correct firing sequence on your ignitor block. 1,2,3,4,6,5.

 

[Cashcrazy]

IAC is new and the firing order is correct. Any other ideas? Willing to test anything. Also, I am going to check fuel trim info in a couple days.

 

[Cashcrazy]

IAC is new and the firing order is correct. Any other ideas? Willing to test anything. I will get fuel trim data in a couple days

 

[plasticseng]

Is it missing, or just not maintaining speed?

 

[Cashcrazy]

Feels like a miss or shudder at idle and it's not constant.

 

[Cashcrazy]

I'm getting into uncharted territory diagnosing with computer data. My background is with old hot rods so I really appreciate any help offered. I took a snap of the fuel trims with an engine at operating temps. I assume the LT numbers are from the ECM and not the app I am using to monitor it. Anyone see anything odd from these percentages?

 

[plasticseng]

I'm not seeing anything.

 

[Cashcrazy]

Sorry. Double post

 

[plasticseng]

That doesn't look too bad. If they are inside +/-10% total (STFT + LTFT), the PCM considers it normal and won't throw a code.

Both of the long term trims being to the negative means it is taking some fuel away compared to the default parameters. In other words, it is sensing a rich condition at the oxygen sensors. The fact that both banks are about the same means it is less likely to be something like a leaking injector and more likely to be something would affect both banks, like a MAF sensor. Another possibility is a temperature sensor reading wrong, tricking the PCM into not seeing the numbers it expects from the O2 sensors.

 

[Cashcrazy]

I sprayed fuel injector cleaner around the intake in the areas I could reach with the straw and no change in idle. Maybe it's a bad injector. They are a little expensive to change without knowing it's that for sure.

What temp sensor are you referring to? I'll replace it if it's cheap.

 

[plasticseng]

If it were only one injector, you would see a different fuel trim number on one bank than the other. The PCM controls each side independently. It would have to be injectors on both banks. Both of them being negative and about the same points toward something that would affect both banks equally. They still aren't too bad at -7 anyway. I'll let some pros chime in, but I bet a lot of mechanics wouldn't concern themselves over them too much.

It almost certainly rules out a vacuum leak. They should drive the fuel trim numbers positive, unless there is a 2nd issue also.

The ECT (engine coolant temp) sensor is right on top of the thermostat housing just behind where the top radiator hose comes in. It's an easy swap out and is only about 20 bucks from Rock Auto for the Motorcraft one. What reading does your scan tool give you for water temp when the engine is fully warmed up?

 

[plasticseng]

199 for water temp sounds about right for a stock thermostat. I will try to hook mine up tomorrow and see what it reads, but that doesn't seem to point toward a bad ECT sensor.

 

[Cashcrazy]

I'm at a total loss at this point. I have checked everything I can find googling the issue. I'm going to try some Liqui Moly fuel injector cleaner in a couple of days after burning some fuel out of the tank. Some of the amazon reviews claim people had rough idles cured and engine codes cleared. I don't have anything to loose at this point.

I appreciate your help on this. What year and how many miles on your rig?

 

[plasticseng]

Mine is an 02 with 262,000 on it. I bet you will get this figured out.

 

[Cashcrazy]

I hope to keep it a couple more years. Will you see what your MAF sensor reading is also? I think .7 might be a little on the high side.

 

[Cashcrazy]

After some reading I took the plunge and ordered a new MAF sensor. Everything online isn't true but I read that they can degrade with age. I have had three other sensors go out so I do not doubt this. I also found a couple threads where people were having similar issues and cleaned the MAF with no change. They replaced other parts only to make a full circle to the MAF and replaced it to correct the issue. I'll throw another $50 at the problem for now.