Jeep Wrangler Idle / Cold Start Issues - Need Help!

[wranglertjoz]

Hi,

In need of some assistance here as no mechanic can tell me whats wrong.

When i start my wrangler tj on a cold start, it high revs for about 10 seconds then when you touch the accelerator the rpm odometer goes to the bottom and almost sounds like it struggles to stay alive. Shakes ect. This is all while parked.
I have attached a video to better explain. Also, black smoke comes out of the exhaust drawing this process. Once the car increases its temperature it goes back to normal and everything works fine.


Can anyone help to identify the issue and provide a solution?

https://streamable.com/1k4mn

 

[KCsTJ]

Black smoke upon startup can mean worn valve stem seals. Oil can leak past worn valve stem seals overnight and into the combustion chamber. When the jeep starts it burns the oil making black smoke.
Any engine codes?
I would clean the throttle body with carb cleaner or similar cleaner and see if the idle behaves.

 

[wranglertjoz]

No engine codes. I do have a minor oil leak that has been there for a while with no increasing in the amount that leaks. A few drops a week at most. I will cleaning though. Any explanation for the fluctuating revs? I have been told its possibly the Idle Air Control Valve.

 

[KCsTJ]

No engine codes. I do have a minor oil leak that has been there for a while with no increasing in the amount that leaks. A few drops a week at most. I will cleaning though. Any explanation for the fluctuating revs? I have been told its possibly the Idle Air Control Valve.

Yes. Spraying carb cleaner into the throttle body while its running, will help clean the IAC valve. Try that before buying parts

 

[por212]

Wouldn’t black exhaust smoke be an indication of a rich fuel mixture condition?

 

[Big Red 1]

The IAC valve gets surprisingly dirty. You can spray carb cleaner and that’s fine but I would pull the bowl and valve out. It takes a torx bit with the hole in then center to remove. I pulled mine and it was nasty. I had a high idle of around 1,500 rpm and it took care of it. As far as the black smoke, I would try this part and see if it still does it. Could be unburnt fuel on the high idle on cold start up. But I pretty much had every problem you stated until I cleaned it.

 

[KCsTJ]

Wouldn’t black exhaust smoke be an indication of a rich fuel mixture condition?

Yes but the OP said the black smoke goes away.
If it was a rich fuel condition I would expect the black smoke to continue, especially if the 02 sensor is bad..

 

[Stockli]

Does horn and cruise work?

 

[wranglertjoz]

Horn and cruise work.

I will clean the throttle body this weekend and see how we go. Any recommendations as to whats the best cleaner for throttle body and IAC Valve? Or any standard throttle body cleaner is fine?

 

[KCsTJ]

Horn and cruise work.

I will clean the throttle body this weekend and see how we go. Any recommendations as to whats the best cleaner for throttle body and IAC Valve? Or any standard throttle body cleaner is fine?

Any throttle body or carb cleaner will do.
If you have a chance maybe take a before and after pic?

 

[JSlad]

At cold start mine does a similar thing... it runs high for a bit until it goes into a gear then the engine engaging the trans slows it down, which can't be good. Idle Control Valve and a throttle body cleaning are in my future according to this two year old thread.. lol....

 

[BrunoPizz97]

Check your spark plugs wires make sure their in the correct order on the distributor and are leading to the correct cylinder. Seems like a timing issue

 

[Jerry Bransford]

Horn and cruise work.

I will clean the throttle body this weekend and see how we go. Any recommendations as to whats the best cleaner for throttle body and IAC Valve? Or any standard throttle body cleaner is fine?

Any aerosol can of Throttle Body cleaner will be fine. To clean the IAC make sure the engine rpms are at idle or the cleaner will bypass the IAC. The engine will die when the IAC gets flooded with cleaner but that's normal, just let the cleaner soak for a few seconds then restart the engine and do it again. Raising the rpms off idle will take the IAC out of the circuit so make sure to only spray at idle rpms.

A bad temperature sender (the one next to the upper radiator hose) can also cause idle problems if it is telling the computer the engine is warm but it's really still cold. When the computer erroneously thinks the engine is warm (but it's really still cold) it will prematurely refer to the O2 sensors which can cause a rough idle until the engine actually warms up.