Unstable RPM?!??

[IM OUTTI]

06' 4.2..... I noticed my car usually idles at 800 rpm. But every now and then (while car is in drive) the rpm drops to about 700 and u can feel the engine shake. I also notice wen using the HVAC the rpm (while in drive) idles at 850 and the problem disappears. Very strange but jus wondering have anyone had this issue and wat was the outcome? Thanks in advance guys.

[FormulaElement]

I have had a few random times the car doesn't idle good (feels shakes), it could be a stuck engine mount as they are active and stiffen up at certain times vs others.

My 06 4.2 idles at 600 rpm in drive and at 700 rpm in park and while in drive with the HVAC on.

[IM OUTTI]

I've seen some engine mounts going for $330 each. Any recommendations on a good set.

[kocyk123]

Search the part number in google and you will find them for around $260 OEM. I also have one that needs to get replaced

[ichi d]

Carbon build up?

[FormulaElement]

The 2006 4.2 isn't FSI, and isn't subject to carbon buildup... Well not bad carbon buildup, you can still get a little bit.