Looking for some thoughts and advice!

1999 dodge ram 1500 5.2L.

On start up, in the morning, truck doesn't want to idle at first. I have to keep my foot on the gas for a few seconds, and slowly back it off, and then the truck will idle low (500-600) but will at least keep running and won't die.
After it warms up, it runs like a top all day long, with no problems.

I have:
1. Replaced TPS
2. Replaced IAC
3. Removed and clean TB
4. Replaced all O2 sensors
5. Had the battery checked, battery is strong
6. Checked, and no codes have been thrown
7. Reset pcm

It seems to me, that the truck no longer recognizes it is cold so it doesn't put itself in "cold mode" and kick up the rpms like it use to. It's like it just stays in "warm mode" and wants to idle the truck around that 500-600 rpm range.

Any help would be greatly appreciate guys.
Is there something I am missing here that tells the truck it is cold so it will bring up the rpms?

 

Check for vacuum leaks around the intake.
Have you taken care of your plenum (internal vacuum leak).
See here: https://dodgeforum.com/forum/2nd-gen...um-thread.html
Pull the front o2 sensor and see if it runs any better (indication of clogged cat due to plenum issue).
What's your fuel pressure looking like? An auto parts store will lend you a gauge.

 

when you replaced the IAC, did you check/clean the port in the bottom of the IAC well? if not, do that.

also - does your temperature gauge work properly - showing cold when cold and then warming up to normal. the pcm reads the cold engine temp to kick up the cold idle.

there's another sensor in the front/top of the intake (IAT), intake air temp sensor. I don't know what the pcm does with it, but if you know someone with a scanner, or find a test procedure using an ohm meter, you could check that its reading normal.

 

And how did you reset the PCM?

The IAT is used simply to help the motor when it is cold out, and for emissions purpose. I bad IAT CAN cause idle problems, but they rarely go bad.

First check the temperature sender for the PCM, if it is off, engine will never idle right.

 

All gauges do appear to be functioning properly.
I did clean the port/well of the IAC. I know it is clean.
I have not checked fuel pressure yet. That is on my to do list.
I thought about just replacing the IAT as well, just to rule it out. I have just never heard of one going bad!

You mention making sure the temperature sender is functioning properly for the PCM, are you referring to the coolant temp sensor?

I am going to need to borrow a guage from the auto parts store to check fuel pressure. I think I will just pick up a coolant temp sensor and IAT sensor from the part store while I'm there. There inexpensive enough that I can at least rule them out if anything.

 

fuel pressure is unrelated to idle speed problem. you can check it if you wish, but its not going to help this problem.

i've also never heard of an IAT going bad, but I don't know how the truck would react if it did, or how to test it.

if IAC port is clean, and IAC pintle is not moving in/out to change idle speed (you can see if from the top side of the TB), then either the new IAC is bad, or wiring, or PCM is not commanding it.

don't operate the IAC outside of it's well. i tried that one time and it spit the pintle completely out.

if IAC is not working right, either test the wiring, or try replacing it again.

 

Yes temperature sender is referring to coolant temp sensor.

 

Thanks for the information guys.

I decided last night to pull the new IAC back out, and put the old one back in, after I cleaned it up really well with TB cleaner. For the first time...in a long time this morning, the truck fired right up and idled perfectly as it should. When I was putting the old one back in, it appeared that the new IAC pintle wasn't extending out quite as far as it should, about 1/8 inch shorter than the original iac pintle. I'm thinking/hoping this was the problem. I'll keep an eye on it over the next few days and see if it problems comes back.

I'll be happy if this fixes it, but also a tad upset that the problem all along might have been this new IAC. I guess that is a risk you take when buying non factory parts for these mopars!

I think I will wait on changing out any temperature sensors now until I see if this in fact fixes it.

I'll keep you all posted

 

actually, when the pintle retracts into the IAC motor, it opens the port in the bottom of the well, lets in more air and idles faster.

when the pintle extends out, it closes up the port in the bottom of the well, lets in less air, and idles slower.

so all other things being equal, a shorter pintle would cause it to idle faster...

but, these stupid little IAC's are fragile as hell, impossible to test, and not worth fussing over. if your new one is covered by a warranty, exchange it for a new one. tell them the damn thing quit working, which is true.

 

Well guys, believe that in fact fixed my problem after all!

Appreciated everyone's help and insight!

Thanks

Case closed.