1998 2.5 with erratic idle

[P man]

1998 2.5 138K miles. The idle is erratic meaning it goes up and down..from 2200 down to 800 and then back up. It started the other day out of nowhere with a stumble and a check engine light.

I have done the following

Cleaned IAC and reinstalled no change
Swapped in a used IAC made it worse
Swapped the TPS with a used one I had no change
I have checked every inch of vacuum line and isolated the engine from the heater to make sure it wasn't leaking behind the heater box no change

I checked the manifold bolts and they are all tight. The throttle body bolts are tight and the gasket is new.

What am I missing? What do I check next? I'm tempted tempted buy a new mopar IAC

 

[Jerry Bransford]

Does that problem occur right after the first start of the day too when the engine is still cold? Does engine temperature seem to affect it?

 

[P man]

Does that problem occur right after the first start of the day too when the engine is still cold? Does engine temperature seem to affect it?

It seems to be happening more when cold (before t-stat opens) but has happened at operating temp as well

 

[Jerry Bransford]

If the engine temperature gauge is where it should be, another possibility is the IAT (intake air temperature) sender is bad. It is screwed into the intake manifold.

 

[P man]

If the engine temperature gauge is where it should be, another possibility is the IAT (intake air temperature) sender is bad. It is screwed into the intake manifold.

Ok ill swap the IAT with one from a parts jeep and see what happens...the temp gauge has stayed normal