I have a 2004 MT RX8, 80k... and recently I have noticed when I'm at a stoplight with the AC running I will get an erratic idle. Sometimes shaking the car so violently that I feel the necessity to shut down the AC altogether... when I do that it seems to go back to a normal idle. My thoughts are its a cracked engine mount is causing this... I really don't know what else would cause such a violent shake when I engage the AC pulley. I do have an under-drive pulley, but I highly doubt it plays any factor into this. I'm sure others have had this problem and brought it in, so I'd like to know what was said needed to be done to fix it, etc. Is this something I could do myself?

 

The idle does change with A/C and even with the cooling fans on... But if it's gotten really bad then it's probably engine mounts. There's a test you can do in this TSB
http://www.finishlineperformance.com...01-09-2062.pdf

 

I keep meaning to see if I can get this replaced under warranty as my car does the same thing...