Shaky Idle

[03hothemi]

Hey all!! I've been lurking around for a while, and found some very useful information here at yall's place. But, now, I have an issue that so far my searching has yet to resolve.

I've got the dreaded shaky idle syndrome, that seems to plague nearly every 4 cylinder car that I have ever driven. Thinking it was just me, and my inherent distaste for 4 cylinders (been brought up on mostly big blocks and diesels), I drove a friend of mine's 06 PTC touring car, and low and behold, it idles smoother that my Hemi Ram.

Here's what I've done so far on my 05...

1) I'm the second owner of this car...picked it up from a Chrysler dealer with less than 20 k on the clock in 06. Car now has just over 51k on it.

2) Oil change every 3k religiously

3) New plugs, champion plats, and wires, Tailor mag, 15k ago as a tune up.

4) Car began to idle rough and over heat a little and AC blew warm about 5k ago.

5) Replaced cooling fan, fixed AC and overheat problem, kinda fixed rough idle.

6) replaced wires again(after reading several posts here) with Orielly auto wires did not change idle prob

7) Ran 2 tanks of b-12 injector cleaner thru it with no change

8) sprayed ether around all intake gasket (upper and lower) areas and around all vacuum lines and found no leaks

9) checked and cleaned pcv valve earlier this evening with no change at all.

Seeing as how I have completely run out of ideas, is there a PCM flash, or something I am missing?

The rough idle is always there, but is more prevalent after the car has warmed to operating temp and even worse when the AC is on. There has been no decrease in overall performance nor have I seen a mileage drop (still consistent at 27 combined). I'm at a loss here and, quite frankly, getting a little perturbed at this car. I love it, and my wife loves it, but if I can't get this figured out, I might have to do something drastic...like beat my head on the wall or something.

Sorry for the long first post, but thanks in advance for any and all help!

[quicksilverdon]

Originally Posted by 03hothemi

3) New plugs, champion plats, and wires, Tailor mag, 15k ago as a tune up.

Is the "Tailor mag" a replacement coil? Put the stock one back.
I don't believe it would cause bad idle, but what did you gap plugs at? Should be 0.040
Do a search on IAC (Idle Air Controller) - try cleaning that.

[CREWZIN]

I agree with QSD, especially the plug gap. The stickers on the car say .050in but Chrysler came out with a Technical Service Bulletin (TSB) telling everyone to drop the gap to .040 which would solve a whole host of problems.

Also as QSD noted, the Idle Air Controller (IAC) located behind the Throttle Body can be taken off and cleaned or just replaced. Dirt can accumulate in the IAC and hurt the idle.

[ChefTank]

My sister has a 06 NA, had the same problem. We swapped the coil and it stopped. I gap my turbo at .032 but am running higher boost. We gapped hers at .038.

[03hothemi]

The 'Tailor mag' I referred to in my first post are the wires. I haven't tried to change the Coil yet.

I pulled and cleaned IAC valve this evening...to no avail. Gonna go pull plugs and check gaps, but I thought I gapped them at .040. It's worth a shot.

[quicksilverdon]

Damn. You've covered all the common causes.
Other thoughts:
Motor mounts - I've read of some failing.
There are counterbalance weights in the crankcase - driven by chain - could that have broken?
How bad was the overheating you had? Did you lose coolant? Did gauge go into red? I'm thinking minor head gasket leak...
One or more injectors could be acting up - there's a "spray pattern" test that can be done - don't know what that costs...
Dunno...

[Sharkstooth]

You said you fixed the overheating problem by replacing the fan,but did you replace the head gasket.It is possible that you have a leaky head gasket causing the idle miss and if you think about it when it warms up the aluminum expands and the leak becomes worse causing it to run worse.The reason why i say this is because i had a car that did this and did not show signs of it like smoking or smelling like antifreeze,than all of a sudden it got worse and would go through a gallon of water a day and still would not smoke and had no water in the oil and the car still had great power.When i took my camaro apart,it was leaking out of a little water jacket hole in the head gasket.I put back together and the Idle problem and losing water where fixed.I know these are two different cars but the same concept,good luck.

[03hothemi]

Originally Posted by quicksilverdon

Damn. You've covered all the common causes.
Other thoughts:
Motor mounts - I've read of some failing.
There are counterbalance weights in the crankcase - driven by chain - could that have broken?
How bad was the overheating you had? Did you lose coolant? Did gauge go into red? I'm thinking minor head gasket leak...
Dunno...

Well...I'm not a novice at this stuff...but I ain't no pro neither...i guess that's why were all here. It seems that a collective of minds can solve just about anything...other than in politics and religion, right?

I've considered motor mounts being bad. The only problem I see with that is that the motor itself shakes, but it never shook this much at all. Failing motor mounts would tend to transfer what I believe to be much more of the roughness into the car than what is actually occurring. By the way, how much should the motor move when the car is put into gear?

I really hope that internally this motor is sound. I would suspect that if counterbalance weights were off that I would feel the vibration throughout the entire range of RPMs, not just at idle. Once the car comes off of idle, it is perfectly smooth. No hitch in it's get-a-long whatsoever.

The car never actually overheated in the since that it ever lost coolant. The gauge never went red. I have to say, my wife keeps a pretty sharp eye on her gauges. And, I have noticed no coolant loss in the past few months, other than what was lost and replaced during the fan replacement.

Funny thing...the sticker on the car says .040. When was the plug gap spec changed? Just out of curiosity more than anything. I just re-gapped the plugs. All of them were at .060 plus. It looked like the plugs have been in there for 100k but I know damn well I put a new set in last summer. Oh, and by the way, I lied earlier. I put champion plats in my truck, and autolite plats in the PT. I'm gonna go later this week and buy a new set of champs for the PT and see if that solves the issue. I did notice that after setting the gaps between .038 and .040 that the idle did somewhat smooth out, but is still rougher than my friends 06.

Any other ideas?

[03hothemi]

Originally Posted by Sharkstooth

You said you fixed the overheating problem by replacing the fan,but did you replace the head gasket.It is possible that you have a leaky head gasket causing the idle miss and if you think about it when it warms up the aluminum expands and the leak becomes worse causing it to run worse.The reason why i say this is because i had a car that did this and did not show signs of it like smoking or smelling like antifreeze,than all of a sudden it got worse and would go through a gallon of water a day and still would not smoke and had no water in the oil and the car still had great power.When i took my camaro apart,it was leaking out of a little water jacket hole in the head gasket.I put back together and the Idle problem and losing water where fixed.I know these are two different cars but the same concept,good luck.

Very interesting...I did not replace the head gasket. Nor did I consider the possibility of it needing it. I may need to get my buddy to loan me his cooling system pressure tester...

Oh yeah...my wife says I need to put a pic of her car up here, not my truck

[mopar_man]

Here's one check for the head gasket without tool requirements: let the engine cool to stone cold. Remove the radiator cap and start the car. See any bubbles in the coolant? Besides doing the pressure check, you might want to borrow a compression tester. You sure have pulled up a dandy problem here. It'll be interesting to see what it finally ends up being.