Idle question please

[CiCi]

99 Yukon: Replaced IAC a year ago due to excessively high idle, ran great for 2 weeks then idle dropped very low, 500rpm most recently actually stalling when putting into PARK. Just replaced IAC, cleaned throttle body and replaced plugs and wires about 2 weeks ago. Has been idling sort of high but today idle seems higher, upon crank this afternoon idle went over 1000rpm then dropped under 500 then back to normal. What else should I check please, appreciate any help.

 

[zomeizter]

CEL illuminated? Ensure there are no vacuum leaks.

 

[CiCi]

No engine light. Checked for leaks when changing IAC but will check again this weekend. Engine control computer was outchanged about 7 months ago as well.

 

[CiCi]

Changed air filter on Sunday and to date no idle surges.

 

[God]

I'm pretty sure RPM's are supposed to surge up over 1000 upon startup. Then settle

 

[nimrod.sixty9]

I'm pretty sure RPM's are supposed to surge up over 1000 upon startup. Then settle

yeah, Im kind of thinking this is normal operation as well.

 

[CiCi]

god & ******.sixty9: I agree a slight surge upon crank is normal but for the idle to drop very low, 300 or so then surge high, over 1000 before dropping to 650 - 700 concerns me and after changing air filter it was perfect for about 4 days and is now doing the same thing. I'm at a loss as to which direction to go now.

 

[kcb37]

I was going to say the same thing. Normal. Even 1500 rpm little higher or lower.
However it should gradually decrease to normal idle. Speed depends on temp, etc...

But for it to rev up, way down, back up, then settle in.
Think your started in the correct direction.
Did you take the throttle body off? How is the gasket?
If you have a vacuum pump may not be a bad time to check for leaks.

 

[CiCi]

kcb37: When I replaced the IAC I took the TB off and cleaned it and the gasket looked good, no breaks. TB was filthy on the botton but the top was pretty clean. Guess I will start going over the hoses and what not. Someone else suggested the TPS but other than cranks the idle is normal. Much better than before the IAC replacement when it was stalling. Thank you