350 idle hunting.

[KingDuramax]

Got a 350ci in a 90 Suburban that the idle goes up and down on. It almost stalls out then goes up to 1500rpm then down again? What is causeing this?

 

[southernspeed]

Open or closed loop?
In open loop could be an air leak or sticking / blocked IAC valve. If it's in closed loop it may be an O2 sensor, coolant sensor or IAC.
Throwing any codes? Done any work on it recently?

 

[KingDuramax]

Not sure if it is in open or closed loop. Does it as soon as you fire it up. Check engine light dosen't come on. Didn't do any work on it. It just started doing it one day.

 

[southernspeed]

Open loop then. That rules out the O2 sensor and coolent sensor. So it may be a distributor prob or IAC valve problem.
Do you have WinALDL? If so run it and see if it gives any clues. If not, take out the IAC valve and clean the pintle and the passage into the TB. See if that helps. If you're lucky DYeager will pick up on this and lay some of his wisdom on ya!

 

[KingDuramax]

Thanks for the help. I'll clean that sometime this weekend and see what happens. It has been sitting for a couple of months.

 

[Thunder]

Check thr TB base gasket . Pretty common for them to go out and cause idle problems. Also check for other vaccum leaks in hoses, lines ect.

 

[KingDuramax]

Cleaned IAC and it idles correct. Thanks for the help.

 

[southernspeed]

Cool....another CK5 success story!!!