High / Fast Idle

[mnewman]

I did a bit of searching and tried some stuff to no avail. I have an '88 2.9 w/auto. As of now it will not idle below 1600 RPMs. I drove it, ran fine, parked it and the next morning I have this problem. Vac lines aren't leaking. Swapped MAP sensor off a good running truck. Same result. Unplugged IAC and idle stayed high. Am I still looking a vacum leak? I sprayed brake cleaner at the base of the intake but didn't get any change in RPM. What else should I look at?

 

[Dirtman]

Pull the IAC valve off and verify that it is actually closing. They can get gummed up and jam open. If thats not it then you almost certainly have a vacuum leak.

 

[mnewman]

Nailed it. I didn't know those went bad like that. Everyone I've had die always dropped the idle. Thanks!