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WJ engine unstable idle speed and then stalling when warm

Hi there,

Jeep Grand Cherokee 2000 4.7

I am trying to help my electrician figure out what could be the issue with the engine’s unstable idle speed and then stalling when warm eventually.

Long story short, I took car to the electrician because the car didn’t want to start for most of the time (when the engine was warm mostly). I needed usually to remove and put back back battery cables, then it would reset and start straight away. So the electrician had an idea. He added his custom-made module, which did reset everytime something in the ECU and then the engine could start easily. Then after a few days, a sudden issue with idle arose. (even when we removed that module it didn’t fix the idle issue)

When the engine is cold idle starts to go up and down (by a fraction) and then when the engine reaches operating temperature and when I stop (either in the drive mode or parking) the engine just dies. Not all the time, but I would say 80%.

When the car is in parking and the gas is pressed a bit to keep (rpm) up, the engine won’t die.

Following things have been changed so far (some things twice to be 100% sure it is not the sensor)

-camshaft sensor (twice)
-crankshaft sensor (twice)
-tried another ECU (we thought that this was the issue for starting and idle but it wasn’t)
-idle air control valve (electrician cleaned that, but we didn’t replace to a new one)

Following things that we could try:

  1. We are thinking to replace wires to the camshaft and crankshaft sensor, perhaps that could be the issue?

  2. Not sure but perhaps MAF (mass airflow) sensor should be replaced as well?

  3. Also thinking to replace the ‘idle air control valve’ with a brand new one.

What are your ideas guys, what should we do next? I am not worried that much about the engine starting issue (since the module can fix that) but the idle issues are the biggest issues right now.

Thank you for your time!

First you need to diagnose this thing. That means narrow down the cause of the problem so you aren’t just replacing random parts which will get expensive, as you are already finding out. This starts with making sure your battery tests good and charging system works properly. Then visually check all the connections you can find under the hood. Then have the fault codes retrieved from the Jeep and post them here. At this point you might also check for vacuum leaks in the engine. You should never have to add some kind of foreign module to make it run right. This Jeep is designed to run properly. All you need to do is find whats stopping it from doing that. Post your engine codes here. Another free attempt would be to properly clean the throttle body.

Agree with @tcmichnorth. Your idle symptoms point to a bad idle air control valve. The reset problem is a different matter. Disable that “kluge” added by your electrician so you can get the error codes.

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Replace the idle air control motor, it will solve both of your problems.

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I will get codes and post it here. Thank you!

You mean we should replace idle air control motor but not the sensor?

by auto electrician, do you mean a guy who rebuilds alternators, starters, and such things?

Or do you mean a guy who diagnoses and fixes wiring problems?

In either case, that’s not who you want . . .

You want a mechanic, specifically a guy who’s decent enough to diagnose and repair drivability problems

That obviously rules out Pep Boys, Just Tires and other such franchises

A reputable independent shop should also be able to lick this once and for all

A 2000 Jeep Grand Cherokee was common as dirt at one time . . . no offense intended

Replacing the IAC once would have cost you far less money than replacing the CMP twice, the CKP twice and the PCM

I’m not familiar with this auto electrician of yours . . . but it sounds as if he’s in over his head

For what it’s worth . . . I agree with the others. Your Jeep has the classic symptoms of a bad IAC

When you replace it, make sure the new part comes with a gasket. I’m mentioning this because some manufacturers . . . Ford, for example . . . make you buy the gasket separately

That said, I believe any decent aftermarket IAC will come with a new gasket

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db4690 - thank you for your reply.

IAC you mean to replace as a whole or just sensor?

IAC = idle air control valve

just replace it, along with that new gasket I mentioned

Forget about the other sensor(s) for now

a bad MAF can lead to stalling . . . but it’s better to try one thing at a time, in my opinion

And at the moment, your symptoms appear to be more consistent with a bad IAC

Now what about those fault codes . . . ?

Knowing what you have/had would help :smiley:

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Hi guys,

I am looking now for another mechanic since the current one couldn’t figure out the issue with engine stalling.

While I am looking for someone else, I’ve scanned jeep with a mobile app. It did found some errors.

It found the following errors: P1391 and P0340

Here are the screenshots from the scanner:

https://i.ibb.co/MDLPcbN/3.jpg - error codes

The rest of the screenshots can’t attach here, since it says I am a new user.

What could be the issue? Camshaft sensor was replaced twice…

Hi,

Indeed there are some issues between CMP and CKP signals, what I have been told by a mechanic. He checked cables in the engine for those sensors, and it seems fine there.

He said that it might be a really expensive, fix. They will investigate further after the holidays.

In the past, he had a similar case with cable issues and the owner had to sell the car because it was not worth it to invest the money.
I guess it’s down to how much I am willing to spend on this old car. It was meant to be used for the off road anyway.

Also here in Europe, it’s super tricky to find those cars.

I will update you soon on what they found out, perhaps it is not that bad. (hopefully) :slight_smile: