Idle RPM Plus Problems

I've noticed sometimes when i start my car in the driveway that when i put it in reverse to back up further in the driveway the rpms will drop to 300 and the engine will vibrate like it wants to die then go to 500 rpm. Also when i rev the car (sometimes) I will release the throttle and the rpms will go to about 400 then back up to 550 or sometimes 600. I've also noticed that my car will idle at stoplights at 500 to 550 rpms. The car has about 76500 miles on it.


The only engine mods I've done is an Airaid Cold Air Intake, and a poweraid throttle body spacer, and i've replace the stock exhaust with a flowmaster 40 series.

Bump, Need input :)

those trucks pretty much and gm idles at about 600 rpms, my blazer, my dads 95 half ton and my moms 2002 grand prix, all gm's ive seen idle at 600

check your PVC valve and vacumm lines first.

http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/12/aa/ce/0900823d8012aace.jsp