Won't idle when hot.
 

I've searched some and cannot seem to find a good answer. My truck was running a little hot (like on the white line just before the red mark) so I stopped driving it last fall and let it sit till I had time this spring. Prior to that, occasionally, when it was hot it would stall at idle. The truck would always restart, and if I use the foot on brake and gas method I could always get it home. I did start it once a week over the winter and drive it a block or so and let it reach close to normal temps.

Today, we finally got a chance to work on it. We replaced the thermostat, the coolant sensor (which was actually physically broken on the top where the wire connects) the Idle control valve, and the TPS. We've also within the last week replaced the spark plugs and air cleaner.

The truck will run normally, with plenty of pickup for something with 249,000 miles and idle. As the truck approaches 200 degrees, it ceases to idle and stalls. You can still get it to start by giving it gas, and again it will run and shift normally until you let off the gas and then it will stall even going around a corner.

Also we hadn't driven it far yet but I'm not sure it's still not going to run "hot" if we drove it very far I saw temps of over 200 on the dash gauge and 220 on the system scanner I had on it while driving it.

Has anyone experienced this and possibly be of any help?

Thanks,

Deach

I would suspect the iac valve first, usually a cleanout is all that you need but in this case check its operation.

In the original post I mentioned I replaced the idle control valve if that's what you're talking about. Is that what you mean by IAC?

Yes. What brand did you use?

What I meant to describe was that when the engine warms up it goes into "open loop" where to computer fully takes over. Here the idle air control should lower the idle speed. There might be an issue with the idle speed going too low and stalling the engine. There is a way too manually adjust it, but there is a certain way to do it so it will work correctly with the computer. This operation should be on the internet somewhere.

One from the auto parts store. I don’t recall the brand. I know it says to use original dodge ones but couldn’t find one on Sunday. Wouldn’t it be odd to have a replacement exhibit the exact same symptom only when the engine warms up?? Ok just asking.

Closed Loop. :) Open loop, the PCM operates off of tables to decide how much fuel to give the engine, how much air to allow in at idle, and when to fire the coil. When the PCM goes in to close loop, (engine above something like 108 degrees, O2 sensors ready, etc.) the PCM uses the O2 sensor to determine how much fuel the engine gets. It will also lower the 'target idle'..... as the engine doesn't need to warm up any more. (It will warm naturally anyway.) PCM will stay in closed loop for the most part, unless it sees throttle past 50% or so, then it will drop back to open loop. (which runs abit richer.... less chance of detonation, and blowing holes in pistons if the O2 sensors are quite as accurate as they should be.)

I put an aftermarket IAC into my truck because I was having some issues. It made things worse...... I had another (used) IAC from another motor laying about (genuine mopar IAC....), so, swapped that one in, reset the PCM, and my stalling problems disappeared.

O.K. So for manually increasing the idle speed screw, just how to reset the pcm?

You can set minimum idle with that set screw...... but, that may confuse the PCM somewhat. If you just leave the PCM disconnected for a bit, turn the headlights on/off, that will reset it, and it will learn the new zero value for the TPS.

That 'fix', however, isn't a fix, it's a workaround. It may or may not work. The better plan is to fix it correctly, and be done with it. First step in that, is get a genuine mopar IAC. Yes, they are more expensive, but, they actually work right..... I can't really say the same for the aftermarket fellers.