Rough idle when cold - JeepForum.com
 
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post #1 of 10 Old 09-08-2019, 02:53 AM Thread Starter
Kedor
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Join Date: Sep 2019
Posts: 5
Rough idle when cold

Hi everyone

Apologies in advance for the long post, I'm experiencing a problem to which I cannot find a solution, and I think the devil is somewhere out there, in the details... So here it goes !

I recently bought a used Jeep Grand Cherokee Limited edition (5.7 Hemi - 2005) from Germany. The previous owner acquired it when he was in the USA and brought it with him when he moved to Europe. Mileage : 60 000 kms, or about 40 000 miles. The car was barely driven in Europe, as only the guy's wife used it, only in winter, and only locally (to drive the kids to school etc). Due to it being barely used at all, the car was not serviced very thoroughly, with engine oil and other vital changes happening only every 3 years (the yearly mileage of the car over that period is less than 2000).
Upon buying the car, I had a mechanic look at it, and here is what he found : some minor things with the front suspension (bearings and shock absorbers) and most importantly, faulty ignition on two cylinders as well as high tension on a flywheel solenoid. Otherwise, the car starts and runs smooth and behaves as good as new.
I drove the car for about 500 kms (about 300 miles) and saw that when cold, the car had a really rough idle but once warm, it's perfect. So I went to the mechanic, and we did the following:
  • change the engine oil (5W40, more adapted to the local climate and identical to what the previous owner used back in Germany), with new oil and air filters
  • flush the gearbox, including front and back differentials
  • change the ignition coils, sparks and cables
  • clean injectors (ultrasound cleaning)
  • change the battery and recondition the alternator (so it generates a steady 14 volts)
  • take out both catalytic converters temporarily

On Friday, I drove it away from the mechanic, who said the problem was solved. Well, guess what.... Yesterday morning, after a good night to get cold, the problem is still here.
From what the mechanic says, it's all odd cylinders (1, 3, 5, 7) that misfire or somehow do not behave as they should when cold. The catalytic converter was completely clogged (which is possible due to the faulty ignition sparks it had when I bought it). Cylinder pressure is ok on all cylinders (10 bars). Electric tension on sparks is normal as well.
I am short on other possible causes, and so is starting to by my mechanic. Could it be a fuel pump ? Could it be something else ? I've got a check engine light again since yesterday, so I will be able to get the code this week, but if anybody has any idea, I would be grateful for it !

Thanks a lot in advance for reading so far and for any support

Jan

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post #2 of 10 Old 09-09-2019, 09:01 AM
Raffish
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Join Date: Mar 2017
Location: CowTown
Posts: 436
Sweet low milage find!

Post the codes.

Put 5W-20 in it like the manual says..

Check exhaust manifold bolts, especially the back few on both sides. (You can see them if you take off the wheel and liner). If the heat shield moves at all probably have broken studs. If you need to do them order studs and bolts for an '09 as they had a corrosion resistance upgrade that year and are the same size), cheap on Rockauto..

Have you checked fuel trims? (LT is prob well up if manifold bolts are shot).

What plugs did you put in? Should be copper....

Add a catch can, Hemis have nasty blow by system, and clean your throttle body. Back of the butterfly is probably cacked with crud. Others have posted issues with disconnecting the throttle body but I have done it several times with no issues. (Just use some rubbing alcohol and soft rag to clean)

Let us know what you find and post a pic!

05 WK Limited 5.7, QDII, OME HD, 265/70/17 1.25" Spydertrax, CC, MBRP SS, 250xxxkms
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post #3 of 10 Old 09-09-2019, 12:41 PM Thread Starter
Kedor
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Thanks for the reply ! I will try to answer point by point.

The previous owner used to put 5W40, supposedly because it's more in adequation with local climate and driving conditions, says my mechanic. He used the same engine oil, adding that it's not great to use different oil specs. Anyway, the problem was here before I had the oil changed.

I am not entirely sure I understand what you mean with the exhaust pipe bolts. The exhaust does wiggle (well, the visible end of it), but I assume taking out both catalytic converters did not help... But if it was exhaust related, would it not be constant, and not only when cold ?

I am not certain my mechanic checked fuel trims, and I for sure did not. I actually bought a cheap diagnostics scanner yesterday and I'm only discovering how it works. I did read some codes though (see below)

My mechanic used NG LZTR4A-11 spark plugs. From what I see, it's nickel, not copper. Then again, if that was the source, would it constantly occur only on the odd bank ?

So, here are the codes I got yesterday at first scan (all "stored"):
- P0300 : random/multiple cylinder misfire detected
- P0700 : transmission control system (MIL request)
- P0132 : O2 sensor circuit high voltage bank 1 sensor 1
- P0043 : HO2S heater control circuit low bank 1 sensor 3
- P0107 : manifold absolute pressure/barometric pressure circuit low

Then, I tried to make a new scan today, after firing up the engine (and getting a nice rough idle):
- In "stored", all of the above + P3538, P3239, P3543 (no description for either)
- In "pending", P0300, P0430 (since I have both catalytic converters out, not a surprise), P3538, P3239, P3547
- In "permanent", C3F0A

I can't say what order the codes appeared. Upon connecting my scanner to the diagnostics port, it asks whether I want to connect to ECU0 or ECU1, hence I may have missed something yesterday. Also, here is a screenshot of the only live measure I made with my scanner so far, for lack of better judgement. Green curve is the pressure of the intake manifold in kPa and orange curve is speed. The whole thing lasted little over 20 seconds, from ignition to really rough idle.

Does it make any sense ?
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post #4 of 10 Old 09-09-2019, 02:37 PM
Raffish
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Location: CowTown
Posts: 436
What climate are we talking about? Europe is fairly similar to Canada... I'd put 5W-20 and copper plugs in as recomended. Put 5W-20 in and then do another oil change in a few weeks and you shouldn't have more than a few drops of old stuff left inside if worried.

Exhaust manifold bolts are a common Hemi failure, where the manifold connects to the engine.

What scanner did you get? Can you see the Transmission Control Module (TCM)? P0700 is a generic tranny code and will have a specific code hiding inside the module.

You have a good charge on your battery? Low voltage will cause a plethora of seemingly unrelated issues.

Pull the PCV valve ans see if it rattles (or just replace).

Replace MAP sensor.

05 WK Limited 5.7, QDII, OME HD, 265/70/17 1.25" Spydertrax, CC, MBRP SS, 250xxxkms
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post #5 of 10 Old 09-10-2019, 01:21 AM Thread Starter
Kedor
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I will try to check on the TCM later today. By the way, is there any live measure I could do that would give insights ?

Battery is brand new. I cannot check the charge however, but I assume it is sufficient. Actually, I am trying to find a link between the codes I receive, and I am wondering whether it could not be a bad O2 sensor. They do need to heat up to 350 degrees celsius, don't they ? So if the heater circuit is dead, couldn't it be the O2 sensor has a wrong reading, hence sends a wrong signal to the ECU/MAP ?
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post #6 of 10 Old 09-23-2019, 08:04 AM Thread Starter
Kedor
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Apologies for the long time to reply, I was abroad and could not update.

Here is the update : my mechanic has been looking at it and there is no specific code from the TCM apart from the bad solenoid. The MIL must come from the rough idle, which still persists. At this point, I need to use the car for some motorway, so he advised to actually try and drive it for the 2500 kilometers involved and see if it actually changes anything. From what he says, it might help get the car going and either the problem will resolve by itself (like if there is carbon depot on cylinders) or it will help identify the cause.

I am not reassured with this but on the other hand, is there any reason to believe it would be harmful ?
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post #7 of 10 Old 09-23-2019, 08:36 AM
RCS1300
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Not familiar with the 5.7 but the symptoms of a rough idle smoothing out as the engine warms up may be indicative of a vacuum leak through one of the engine seals. As the engine warms up metal and seals expand, closing the vacuum leak. That is where I would start on a 14 year old vehicle.
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post #8 of 10 Old 09-26-2019, 07:22 AM
RCS1300
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The other things I would be looking at are the possibility of a leaking fuel injector or a leaking head gasket - antifreeze entering the cylinders when engine is off.
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post #9 of 10 Old 09-27-2019, 01:51 AM Thread Starter
Kedor
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I will look at that as soon as possible. Just a question though : it it was a leaking fuel injector, would they not have noticed during the cleaning process ? And as for the head gasket, would it not become worse with the engine heating (meaning I'm driving the vehicle), not better ?
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post #10 of 10 Old 09-27-2019, 05:11 AM
RCS1300
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Quote:
Originally Posted by Kedor View Post
I will look at that as soon as possible. Just a question though : it it was a leaking fuel injector, would they not have noticed during the cleaning process ? And as for the head gasket, would it not become worse with the engine heating (meaning I'm driving the vehicle), not better ?
These three items could cause your symptoms of a rough idle until the vehicle warms up.

1. A leaking fuel injector could be dripping fuel onto the piston when the engine is not running. After a cold start the gasoline would burn up rapidly but it may take a little while for the injector to begin working better. A cleaning process only deals with cleaning the spray not the seals of the injectors unless the person that cleaned the injectors specifically checked the seals of each injector when under pressure.

2. A leaking head gasket could be dripping coolant onto the piston when the engine is not running. After a cold start it would take a little time to burn the coolant up. A leaking head gasket is very difficult to identify and can go unnoticed for a long time. A few indicators of a leaking head gasket include loss of coolant, clean white porcelain on the spark plug, and air bubbles in the coolant overflow tank. There are several tests but a good one is a cylinder leak down test.

3. A leaking seal in the air intake system on a cold start could draw in un-metered air causing a lean condition that would not be corrected until the O2 sensors warm up and modify the fuel trims.

Most likely is probably #3 but any one of them is possible. For a leaking head gasket or fuel injector you could purchase a $15 micro camera from Amazon and look inside each cylinder for fluid when the engine is cold. To narrow down your search on which cylinder(s) are causing the issue, you could get a scanner that will give you misfires by cylinder and look at those misfire counts on a cold start. That is what I would do. For a leaking seal on the air intake system, the best solution is to smoke the intake to find the leak. A good smoke machine will tell you if there is a leak and then you have to visually find it.
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