1996 Grand Cherokee 5.2L idle issue.

[DemoFly]

I am having a bit of a time trying to diagnose the idle issue on my jeep.

If I start the jeep with a single prime of the fuel pump, it will start and have a high idle that won't drop, and then after it reaches operating temperature the idle will romp up and down between 1100 and 300rpm.

If I prime the fuel pump several times it will start and run fine. I have checked fuel pressure and it is stable at 50psi no matter the scenario.

NOW RECENTLY it will start and die. I have a CEL for P0505 which is IACV, but the the IACV is new and I have tried another from my Dodge Dakota. The truck will only stay running if I hold the throttle down halfway and it will sputter and pop as if it is running lean.

 

[901Memphis]

EGR stuck open?

 

[yonyon]

It's possible that when you're "priming the fuel pump several times" you're also heating up the O2S so it can go into closed more quickly and hide the problem. I suspect you have a lean running condition while in open loop. Check MAP sensor reading and fuel pressure.

 

[Chris142]

pinch off the pcv and vent hose. them remove the oil filler cap and see if that gasket under your lower plenum is leaking.

 

[Thax]

Check the wiring to the IAC , how is the TPS? What brand IACV did you get , sometimes non Mopar sensors dont play well.

 

[artificialist]

Did you clean the IAC passages when you replaced the IAC? If the passages are dirty, your engine will never idle correctly no matter how far the IAC travels.

 

[DemoFly]

Originally Posted By: artificialist
Did you clean the IAC passages when you replaced the IAC? If the passages are dirty, your engine will never idle correctly no matter how far the IAC travels.

Bingo. Thank you so much.