It was pretty warm here yesterday, so I turned on the AC. Felt nice to cool off, until I rolled up to a stoplight, and the car started vibrating so much that I turned off the AC. The idle speed went from about 850 RPM idling with AC, to about 900 RPM idling with no AC. No noticeable vibration with AC off.

Tried to duplicate today, a much cooler day, and the vibrations were less.

Went to NAPA to get any codes, but there were none.

Last Monday had some work done, new brake master cyl, new clutch master cyl, and a fluid flush with DOT 4. Prior to that, I changed the oil and filter and put on motor and trans mounts from TTR. Oh and a new Diehard group 47 AGM battery last week too.

2009 SS manual trans 78500 miles

I've read that the ECM is supposed to compensate for the AC being on. Any suggestions? Dirty throttle body or MAF sensor?

 

Bad compressor or clutch.

 

Go with the cheaper fix first, clean the TB and MAF then see!

 

Why is everybody wanting to replace computers all of a sudden. In this case I don't see the connection.

Yes, the ECM tries to adjust for the A/C. BUT, if it is the A/C that is causing the drag why blame the ECM?

Why not blame your new clutch cylinder? Maybe the tech didn't do it right.
Why not even consider that the A/C clutch and/or compressor are malfunctioning? Problem when it's on, no problem when it's off. H'MMMMM what is the common link?

 

FWIW. An idle speed of 850 rpms shouldn't have anything to do with a vibration issue.
I would be looking at either a compressor problem or mounting bolts/bracket that could be loose.

Another thing that caught my eye from your 1st post. "put on motor and trans mounts from TTR."
Not to question your ability, but are the mounts installed correctly and torqued to specs ? Especially the front mount.
I would double check those front mount bolts and nuts.

 

X2 on the compressor or motor mounts. Doesnt seem electrical.

 

OK, so if 850 - 900 RPM is normal, then the TB/MAF is likely not a significant factor. I'll recheck the torque on my TTR goodies and look for AC mounting bolts.

Donbrew, nobody here has suggested replacing a computer, nobody is 'blaming' the ECM, nobody is ignoring your suggestion/solution of faulty AC components. As much as my wallet hopes that you're wrong, I've got a strong suspicion that you very well may have nailed it. As you quite often do. However, I can see no connection to the clutch master cylinder, or was that something like "why not put new light bulbs in, since you're blaming everything else".

So you're thinking that there is so much drag that the ECM can't quite compensate? Is there a simple way for me to test for drag (remove belt, turn pulley by hand?) or do I need to take it in? Unchecked it's going to have a significant impact on fuel economy, right? Not to mention possible collateral damage when it completely seizes?

 

OK, so 1 year and nearly 10,000 miles later. I can't remember the last time this issue presented. I'm going to say that the TTR motor and transmission mounts just needed a little time to settle in.

 

Ok!