Idle Issue

I have been having an idle issue that has been really persistant. I have posted about it before and have taken the advice which really hasnt helped much (thanks tho). The issue is when i start the jeep in the morning it idles fine (1000RPM, normal i think), as soon as the temp reaches the first white mark the engine starts to hesitate only during idle(idles at 750-800 once warm). At anything but idle the engine runs perfectly fine. The hesitation thats felt might be a miss but i am not sure. When i am in the car i can feel it as well as hear it thru the exhaust like a very slight shudder every sec .

I have tried:
1. Cleaned Throttle Body
2. Cleaned IAC
3. Replaced TPS, Bosch 02, MAP sensor
4. Fixed all Vacuum Leaks and Replaced vac canister
5. Replaced CCV Ventilation grommets and hoses
6. Spark Plugs and Wires
7. Cleaned Distributor and Rotor (bc it was replaced not to long ago)
8. Ran a can of Bg44k and techron + used seafoam thru vac lines

Any ideas or suggestions would be nice, as i have to pass smog in CA soon and i think this might affect it a bit as something is not right.

PEte

Mine used to idle terrible, occasional misses and a hunting idle, had kind of a dead spot off idle. It got better after I cleaned the grounds. It got better after a few trial and error TPS adjustments. It got better after I cleaned the idle air bypass (and the IAC). It got better after the third set of spark plug cables, when I changed to spiral core non resistor cables (kept the **stock** coil to cap wire, tried a spiral core coil to cap wire, ran like chit). Got better after my new cat. Got better after my new O2 sensor. Got better after I cleaned the connectors on the lower left block. Got better when I cleaned most every connector on the top of the motor and the right fender well. Was almost perfect by the time I cleaned the contacts between the coil and ignition control module. Idles really nice now, idles a little low, but doesn't miss a beat, hunt or hesitate. Good luck.
If you look in the FI manual, idle has more sensor inputs than just about any other mode. A whole lot of possibilities for it to screw up.

I know what you are saying thats its not probably one things and that it might be hard to find. I agree..

I have cleaned all the grounds and still no improvement, maybe tom if i have a chance i will clean all the connectors in the engine bay..what do u use ? carb cleaner and a wire brush ?

As far as spark wires, i have always used bosch -- so i dont think thos are the probs.

Anyway i will try and you guys let me know if you have any other suggestions like possible culprit sensors .

Pete

First it would be good to know what year/engine/trans etc... to think about.


Mike R

94 /cherokee/ Aw4 /4.0 I6/231

pete

It shouldn't idle much above the normal 650-750RPM when cold. This suggests a vacuum leak at the intake manifold because as it warms up things expand and then it seals. The easiest way to check is using some running water over the manifold to locate the leak. The idle will drop where the water gets in.

Not sure what you mean about a hesitation at idle. Does it hesitate when accellerating from idle or does it miss running while idling?

An idle miss is usually due to plugs/wires.

If you still can't figure it out and don't mind driving down my way (Irvine/Costa Mesa) I could look at it for you. I am a Jeep tech and have the factory scan tools.


Mike R

Listen to MJR, he is right on.

The quality of the idle when i first start her up (cold) is usually steady and descent. As the jeep warms up the idle drops but also the jeep shudders/shakes every 1-2 secs. It is very slight but isnt normal.

Thanks for the suggestions i will try the water thing and possibly replace the wires.

pete

Mine is doing the same and a quick compression test (cold and hot) told me a valve was sticking. Decarburizing helped (dumping water down the throttle body while revving to clean it out)

carnuck said:

Mine is doing the same and a quick compression test (cold and hot) told me a valve was sticking. Decarburizing helped (dumping water down the throttle body while revving to clean it out)

Click to expand...

Just be careful if you do this or you can hydrolock the motor. Just a little.


Mike R

Well i think i did something very similar to this with the seafoam. I put it down the brake booster vac line. Anyway it helped but not by much.

Today i changed the spark plug wires and again it helped a bit but its still there.

Pete

You might want to try a can of Mopar combustion chamber cleaner, part #04318001ab available at your local chrysler dealer, Iv'e used it several times and found it to be quite effective. At 5 bucks a can it's worth a shot.

One other long shot is the CPS when it's hot. I have had it on my 88 but the 91-up are a little different so it's a guess.


Mike R

well rahter then start a new thread I'll try here if it's ok. Mines a 89 that idles goofy. Just at idle it's fine, but when you blip the throlttle is hesitates and acts like it's gonna die. My other problem is it will idle well for a bit but the then takes off. It will rev and stay reved even when off the gas. Have to push on the brakes to keep it stopped a lights, ect. To fix it I turn it off and let it sit, usualy after the 3-4 off/on try it goes back to normal. Other wise it's just wants to wrap up. I know I have a exhaust leak, but what things should I be checking? Cap, rotor are new, Magnacore wires and NGK plugs that still should be good, changed a few years ago.

89, 4.0 Renix, Auto. TIA

Weasel: "stay reved even when off the gas"

Probably either a vac leak or your throttle is sticking.
If a leak is that bad you may be able to listen for it under the hood.
The other thing to look at is the IAC. One way or another its getting too much air.

In addition to what was done on the first post of this thread by me , i have also changed the following and still have the idle surge thing during warm idle.

1. changed o2 again on warranty
2. changed TPS and IAC
3. New Fuel Filter
4. New Set of fuel Injectors.

Any ideas or suggestions ??

pete