High idle after every start warm or cold

[scubacarib]

So I am helping my friend with a 91 Cheyenne 2500 it has a 350 Chevy he has thrown a lot of parts at it both temperature sensors throttle positioning sensor and idle speed control to me it acts like a cold start high idle after it starts cold then after a few minutes it drops to a normal good idle drive it around the block turn off the key start it right back up high idle for the couple of minutes then it drops to a perfectly good idle it'll do this all day long any ideas would be appreciated thanks

 

[gmbellew]

it will always idle a little higher on first start up, even when hot, just for a bit until it hits closed loop. it should take much longer to idle down when cold.

 

[scubacarib]

It takes a long time every time

 

[gmbellew]

MAP sensor and CTS have a lot of say in target RPM (or IAC position), especially in open loop. if those sensors are good, you might look for a vacuum leak that may go away when the engine gets warm? if you have a vacuum leak, the IAC can't close enough to bring down the idle.

 

[fast 99]

Is there a way to get data? If IAC counts are low it's a good indicator of a vacuum leak.
Check base gasket, temporarily plug vacuum lines. Have seen wrong or bad PCV valves cause that. Intake gaskets, check both top and bottom.