High idle then engine stall, stumped.

[bomper04]

Recently rebuilt my cylinder head due to bent valves, changed out guides, seals and valves. Cranks over and starts but results in a super high idle around 3k then slowly drops back down, stumbles (misfires) then dies. I can rev freely over 3k but once i let go of the throttle, it dies. Possible IAC problem? Cleaned out IAC and changed gasket. Still the same problem. Any guesses?

 

[97gst_spyder]

IAC is not working right. Test it to be sure.

 

[bomper04]

Will do, but do you really think the IAC could be the possible culprit?

 

[eddied118]

Definitely sounds like the IAC my car does the same thing and it threw a code p0505 which is the IAC malfunction

 

[clean96GST]

I've heard of broken coils in the ISC causing similar problems.

 

[bomper04]

Definitely sounds like the IAC my car does the same thing and it threw a code p0505 which is the IAC malfunction

Just wanted to clarify: you car did the something similar to this? Super high idle then stall? Going to test it this weekend.

 

[bomper04]

IAC is okay, resistance tested and checked out to spec. Moves with key on. TPS okay as well, did a voltage sweep and measured just fine. Any ideas? Starts then immediately jumps to about 3k-3500RPM then drops down to about 750 followed by stall. No CELs.

 

[#40Fan]

Can you keep it running around 2k rpms by pressing on the gas? If so, do that and see if a light will kick on eventually. Check your MAF while you are at it.

 

[bomper04]

MAF is plugged in, kept the car running with foot on gas pedal and no light. It's OBD1 so I can't imagine it to be too intelligent . Even switched out IAC with a known good one and same symptoms.

 

[bomper04]

This sucks, figured out the problem today and found a HUGE crack on my intake mani. Covered it up and car ran smooth and idled fine. Darnit. Thanks for the insight guys!