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Running rough at idle only

 
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Old 28 Nov 2010, 08:04 pm
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Default Running rough at idle only

Okay searched the forum and nothing I've found fits what it's doing. To start I'm a diesel mechanic by trade and don't normally fool with anything that is smaller than an 8 liter. Car is a 2003 turbo PT. Came in for p0301 misfire code. Scoped the coil and found wire coming out of number one dead. Replaced coil and high speed misfire gone but rough run at idle still there.

Checked codes and data on scanner and then checked alignment on timing belt. No codes are present but there is 6 degrees difference on gear sync and one cam was off a tooth. Changed timing belt and reassembled. Timing is now dead spot on. Has high end power like never before but still running rough at idle.

One clue which I'm sure is important is the coil burn times. Coil one burn time at idle is between 650-800. Coil two burn time at idle is 1600-1800. If I bring the rpms up to 1200 or more coil burn time on coil one jumps up to what coil two shows. I'm sure the burn time numbers are pointing me somewhere but not too sure where.

We did pull the PCM out and open the cover to take a look. Everything looks okay but one little chip (best thing I can think to call it) appears burnt to me. The gel inside the PCM is very gooey which is in my experience usually a good sign the PCM is crap.

I've also scoped the signals coming to both sides of the coil and the signals going to the injectors. Injectors look okay even swapped injector one with injector two to see if that fixed the problem. No dice. I have also tried using my old propane vacuum leak detector with no surge in engine rpm found putting the tip all around the intake.

Manifold vacuum is a solid 17 at idle measured at the top of the throttle body. Going by my experience a few years ago when I worked on smaller vehicles this tells me there is no vacuum leak.


Any help is greatly appreciated.
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Old 29 Nov 2010, 07:35 am
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Default Re: Running rough at idle only

Wow your the kinda guy we send people to when we can't seem to help owners when they come here, and now your coming here?

You've seem to have done everything and more that we can't do trying to diagnose a problem over the Internet. Taking apart the PCM is way over most of our heads and we've been told Chrysler keeps the secrets of the computer a well guarded secret so it wouldn't do any good to take it apart anyway. Doesn't sound good about the burnt part that you found but don't think that would affect just the idle whatever burnt.

The only 2 things I can add from all the ruff idle problems that come here is: 1) the radiator fan (which has a high rate of failure) isn't cooling off the engine which results is a rough idle. Sometimes it goes along with overheating but sometimes not. You should be able to turn both the low and high speed fan on if you have the right kind of scanner. 2) The ignition parts (plugs and wires) are crap from the factory and we advice owners to change both (with other than OEM parts) as soon as any kind of problems show up. Also, don't use platinum plugs in the Turbo engine as supposedly, the electrode can melt.

Good luck.
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Last edited by CREWZIN; 29 Nov 2010 at 07:45 am.
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Old 29 Nov 2010, 08:14 am
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Default Re: Running rough at idle only

I'm here because I don't normally deal with small gas engine stuff. Asked my manager to bring it over to my house last night and found it is throwing the
P0301 code again but now once it warms up a bit it kinda smooths out. Coolant temp sensor shows to be in specs comparing it readings taken with an IR temp gun. Tosses the genisys on it last night to check coil burn times. They are bouncing now between 658-1800 on coil one and between 1600-1800 on coil two. It starts runnng rough as soon as the burn time drops on coil one. I also checked the fuel pressure to see what it is doing and it's sitting right at 58PSI running at idle. Was kinda weird though when I went to bled my pressure adapter down I got air out of the lines instead of straight fuel. I've got this posted on a couple main mechanic sites to see what they come up with. When I get it solved I'll post the fix here.
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Old 29 Nov 2010, 08:53 am
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Default Re: Running rough at idle only

Right, thanks. As I said, you have all the tools whereas we can pass on what others have been through with the same problem and knowledge from past experiences. When something out of the ordinary pops up there's no way for us to diagnose it other than take a guess.

From what you just said, did you try a new coil just for the heck of it? Lots of different parts in the play to send the coil a signal to shoot a spark to the plugs. Different sensors and of course the PCM are major players. It might turn out to be the computer after all.
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Old 29 Nov 2010, 09:01 pm
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Default Re: Running rough at idle only

Well we had put a new coil on it to fix the original misfire and it got rid of the high speed misfire. Tonight just for the sake of argument I called the parts store and had them send me another coil with new NGK u-groove plugs and a new set of wires. Gapped the plugs at about .035 and reassembled the pain in my butt. It runs alot smoother which makes no sense as the new wires have a higher resistance than the old ones did. Manager is going to drive it for about a week and we'll see if it behaves.
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Old 30 Nov 2010, 01:15 pm
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Default Re: Running rough at idle only

I jumped in too late - I was going to suggest the plugs & wires - since you already checked the injectors and tested for intake manifold leak. That a coil died is relatively unusual.
The stock ignition wires are crap - when they go they can arc from one to another - why more so at idle, I don't know.
Since the timing belt had jumped, I'll bet it runs LOTs better now with new belt.
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Old 30 Nov 2010, 03:13 pm
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Default Re: Running rough at idle only

Sorry to jump in sect... I need help tremendously. I have a 2003 pt (standard trans) Ihave already had to replace the bushings for the linkage and had a timing belt put in at 85000 mi. replaced all three mounts... The car was dying when the clutch was depressed & a/c was on,now I turn the car on(it starts up without hessitation) and it either dies or it idles very rough. I'm not sure what to make of it. I have heard that it could be the IAC on the throtle body,spark plugs,or the timing. ???any ideas???
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Old 30 Nov 2010, 04:05 pm
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Default Re: Running rough at idle only

We are still waiting on the original poster to find out if his problem is fixed.

Yes, you should have started your own thread plus, this is the Turbo section of the forum which sometimes has different problems than the non-turbo. What do you have?

As far as yours, it can't be the timing as you just had the belt replaced, unless your mechanic screwed it up. When was the last time the plugs and wires were changed?

The IAC controls the idle but won't make it run rough.

Does it run rough when you start it up without the A/C on ??
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Last edited by CREWZIN; 30 Nov 2010 at 04:09 pm.
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