[jimbo54494]

'99 Durango with 5.9, about two years ago I had a problem with very low idle and stalling. A new IAC fixed it good as new. Now lately as the weather has turned cooler I have idle problems, but only on a cold startup. Right after the motor fires the rpms only ramp up to about 800 rpm, then fall down to 400 rpm, almost stalls, ramps up to only 800 rpm, then falls again. Usually it will stall unless I give it a little gas to stabilize it. Once it stabilizes it only idles at 600 - 700 rpm. It does seem to idle lower than normal when warm (600 rpm), but it does idle. I'm guessing it is the IAC again, but the last time I had a problem it would not idle at all, now this time it seems that it is halfway trying to work. Once in a while it starts almost like normal, with the motor ramping up to about 1100 - 1200 rpm right after firing then settling down to about 800 rpm. It runs great otherwise, accelerates great, even when cold.

I have just changed the intake & plenum gaskets, but this problem started before I took the intake off. I took off the IAC and cleaned it, I also energized it while it was off and the piston did move, but cleaning it did not improve the situation. It's definitely acting like the IAC is not opening enough, I took off the hose to the PVC valve and the idle immediately picked up 200 - 300 rpm with the extra air leakage into the intake. I'm not getting any fault codes, so here's my order of planned parts changes to see if I can cure it:

IAC
MAP
plugs & wires
O2 sensors
Coolant temp sensor
TPS
PCM

Let me know if you have seen an IAC act like this, and let me know what you think of my order of parts changes. Thanks!

 

[pooperscooper]

that is wierd that when you pulled the PCV off it ramped up in idle. i would check the air filter, and the test the map.

 

[B-300]

It sounds to me as if the idle motor is out of range or sticking, and not going opening completely.
I'm not an expert on the subject, but would try the following tests.
1) Turn on the AC to see if the idle speed changes.
2) Remove the battery ground and idle motor, reconnect the battery while watching the idle motor it might move to a "parked" position. If not then turn the key to on and watch to see if it moves, this will probably require a helper.
3) Check the throttles for correct opening.-If they are closed to far the idle motor won't be able to compensate.
4) Coolant temp sender -Some one else with a TBI engine had problems with there idle due to a bad temp sender.

 

[jimbo54494]

Yesterday it was still acting up, now this morning it started perfectly. Ramped up to 1200 rpm right after firing and then settled into a 900 rpm idle. I agree it is acting like the IAC is sticking at times; we'll see how long it is good for now...

 

[moparram97]

when you un hooked the pcv you creared a small vacume leak which caused your rpms to go up, this is basically what the Iac does it causes a controled vacume leak to raise rpm, at least that is what my mech told me when he described it, I recently had the exact same prob, change the IAC and you should be good as new...

 

[stev]

FYI ---

When the IAC was replaced, did the dealership also CLEAN the IAC port too? Just replacing the IAC is half the repair job!

Seeing that you have a NEW IAC in the TB, you can easily take it out and inspect the port. If the port is gunked with black carbon build up, then the dealership neglected to really correct the problem. I know, I've dealt with this issue twice before.

Please check out a step-by-step with 56k friendly on photos, How to Clean the IAC ...

http://www.dodgetalk.com/forums/showthread.php?t=114679