Rough Idle-Test your trouble shooting skillz

1990 Jeep Cherokee 4.0L Automatic

Symptoms:
Rough Idle
Runs strong, doesn't feel like it's missing
very slight stumble when mild gas is applied at 30-40mph
occasionally stalls(very seldom) when restarted idles at 2000rpm, often very hard to get it to quit.
occasionally(very seldom) will idle at 2000rpm from a cold start, often very hard to get it to quit.

Parts recently replaced in an atempt to fix the rough idle:
Cap & Rotor
Spark Plugs & Wires
TPS
O2 Sensor

Things tested:
Fuel Pressure- normal
injectors- normal

I have cleaned the throttle body and inside where the IAC sits. I have ran several tanks of Chevron Techron.
I do not have the equipment to pull error codes from this year renix. All I have is a multimeter.

Any ideas, suggestions, things I should check?? :wow:

High Idle

I ohad the same high idle problem after cleaning my throttle body and usually happens after every time I clean it. Eventually it clears up. I think it is the IAC but have not got around to changing it. The stumble at higher speeds sounds like a coil problem.

I would agree, but when you clean the TB, I remove it and clean the hell out of it. All the nooks and crannys. Take the IAC motor out and clean that port really good with an old toothbrush. This keeps my 88' from the old man stumble and idle or gas. Juice

I Did clean the area around the IAC, but that was 3 mos ago. I doubt the occasional high idle trouble is from that cleaning.
Is there a safe way to test my coil? Would that cause the rough idle?
The main problem that really bugs me is the rough idle. I mention the other things because they may be a clue. I have put allot of money into my jeep so far and it is really getting there, so the rough idles really bugs me. I know it is probably something simple.

coil test

Get a Chiltons, it will tell you how to check your coil. Go to a auto store and buy a spark tester then test all the wires with the gap set at 3/4 inch. If your coil is shorted it will run good at idle but stumble at higher speeds.

iac

3 months since you've cleaned the IAC on a high-mileage XJ? The seal behind that thing likes to leak spewage, Clean it again, takes 10 mins, costs nuthin.

How often should I pull and clean the IAC? As I said, it made no difference last time I cleaned it. It hasn't gotten any better or worse since then. I seriously doubt cleaning it again will have any different result than last time, as the rough idle was present both before and after the last cleaning.
I will give it a more thorough cleaning this time.
Does anyone have any other ideas suggestions?

rws said:

Get a Chiltons, it will tell you how to check your coil. Go to a auto store and buy a spark tester then test all the wires with the gap set at 3/4 inch. If your coil is shorted it will run good at idle but stumble at higher speeds.

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Idles rough, barely stumbles at high speeds. The stumbling wouldn't be noticed by anyone else but me probably. It's that mild. The primary symptom is the rough idle. By rough idle I dont mean horrible rough, just rougher than it should. I drove another cherokee we had at work for awhile before I bought this one. It idled very smooth in comparison to mine. It's one of those cases where the Jeep is in great condition the engine runs very strong, with no other problems or sypmtoms other than those described.

Talon, an EGR valve that's sticking open will cause a poor idle. Temporarily remove and plug the vacuum hose going to it, and see if the idle changes.

ccv lines all clear?

momma's xj said:

ccv lines all clear?

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you responded to a 4 year old thread