General Maintenance & Repairs - Car randomly idles at 1500 rpm :bang:

I have a 99 z28 m6 and this is getting annoying! Base idle is set around 600rpm and it will just jump to 1500 and stay there. While going at speed if you put the car in neutral it goes to 1500 and stays, untill you come to a complete stop it wont return to base idle, and it doesnt always return to base idle. You can choke it down sometimes and it will stay but not always. Im tired of setting at stop lights with everyone looking at me funny
:soapbox:

Sounds like a vacuum leak to me.

IAC sticking. Did you change the TB recently? Disturb the throttle linkage? Did it start doing this out of the blue?

Does the idle hunt? It could be the IAC is stuck.

IAC sticking. Did you change the TB recently? Disturb the throttle linkage? Did it start doing this out of the blue?

Does the idle hunt? It could be the IAC is stuck.

Havent changed anything just started out of no where. It seems like it hunts a little.

Ok. Check vacuum hoses for cracks, splits esp the PCV routing around the intake. For the IAC cleaning, use a Torx #20 bit and take the IAC out of the TB. Disconnect the electrical (obviously!) and make sure the little "O" ring comes out and inspect it. Clean the pintle of the IAC with TB cleaner spray or a kind of automotive carbon dissolver. Avoid the electrical portion of the mechanism, do not push/pull the pintle in any way. You will prolly strip the worm gear if you do. Look in the TB for carbon buildup while you are there. Reinstall the O ring with fresh motor oil on it (if it is ok) then gently seat the IAC in there and reconnect everything. Screws are to be torqued to a low value(?). There is a procedure for resetting the IAC somewhere on this board too...

Thanks guys i'll check it out after work. :thumb:

Could be the throttle position sensor. Get someone to hook up a Tech II to it and it will tell you what your problem is.