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Engine shudder in 08 LTZ w/ 3.6

8292 Views 18 Replies 10 Participants Last post by  DrivenDaily
I have an 08 LTZ 3.6 that's having a mild shudder while idling. The best way I know to describe it is it's as if the engine is out of balance, if that can even happen. It's not a vibration, but "soft" shudder. It is worse when idling in "D"rive, such as at a stop light, than in "P"ark, but isn't at all noticeable during acceleration or cruising. There is no drop in RPMs or error messages in the DIC. I have looked through some of the threads here, but none of them seem to encompass my issue. I just bought this car a month ago and have it under the GMPP Major Guard Warranty, but I would like to be armed with a little knowledge of this issue in case the dealer tries to tell me they can't replicate it or claim it's normal. Thanks for the help guys!!!
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With the LTZ you get ACC - automatic climate control. It will run the AC compressor without turning on the AC light. You might be experiencing the extra draw on power when it kicks in. To test this theory, next time it shudders turn your fan knob to the "OFF" position to shut down ACC completely. If the shudder stops then it's the AC compressor. If not then that's one component/system you can eliminate as a suspect.
Well, the diagnosis and testing was free anyhow. Sorry it didn't pan out. We have a few members on here who are totally technical wizards. Once they make it to this thread they'll have some input for you.
Possible dirty injectors, but at only 8K miles it shouldn't be. Unless previous owner ran 87 Mom-N-Pop gas all the time, then it might.

Possible bad coil (you have COP) or primary wire to one of them.

Possible PCM/ECM issue, but that's highly unlikely.
I've got the same problem as my I4. I've been to the dealer two or three times for this problem over the last few months and no one can identify the problem, like your's it doesn't throw any codes either.

I noticed today that it shudders more with the temp is over 80. Today we hit 91 and it shuttered at idle most of the way home.

The car also shuttered/missed at an even 75 to 80 mph cruise while on vacation last week. Now that my car is out of warranty I'm going to try an independent mechanic and see if they can find the issue.
I have been told this is the power steering pump running. Very noticeable in the steering wheel.
Just to clarify this thread and the posts that are being made:

The title refers to 3.6 V6 models, not I4.

3.5 and 3.6 V6 engines have hydraulic power steering. Any issues associated with the system will be mechanical in nature.

I4 engines have Electronic Power Steering (EPS). Any issues with EPS will likely be within the EPS motor module. Reading other posts on this site suggests that the motor is not serviceable by DIYers as it needs to be calibrated with specialized shop equipment.
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