I've started having an idle problem with my 95 5.9L AT 1500. I first noticed this problem about a week ago and it seems to be consistently present. I only notice it when the truck is at low speeds when I have had the throttle partially open and then allow it to go full closed. An example would be when I'm in a parking lot space, I crank the truck and it starts and idles fine. I put the truck in reverse, and give it a little throttle to back up. As soon as I remove my foot from the accelerator pedal to put it on the brake the idle will drop way low and often the truck will die. I can immediately put the transmission in neutral and crank the truck back up with no problems. If I'm rolling down the road I can lift my foot from the accelerator and when I come to a stop at a stop light it will return to idle just fine. The problem only seems to occur in the transition from having the throttle partially open to fully closed when the truck isn't moving fast enough to keep the engine RPM up via truck motion.

* I think the problem is only present when the truck is warmed up and operating closed loop.
* The truck has no problem idling once it successfully transitions to idle from having had throttle partially open
* Although I haven't explicitly checked the mileage, I doesn't seem to be any worse than the always horrible 13-14 mpg or so I always get.
* I checked codes and none present in the PCM

I have my suspicion as to the likely cause of this but am not 100% sure and hate to just randomly start throwing parts at it, especially since I'm not planning to keep the truck all that much longer.

Anyone have any thought they'd like to share?

 

Get a Haynes and test the TPS. Also you can try cleaning the IAC. https://dodgeforum.com/forum/dodge-r...n-the-iac.html

Might be a an o2 sensor problem also. Which usually leads to another problem.

 

Could also be a vacu issue.

 

Thanks. You named all 3 of what I figured to be the most likely culprits. I was really sort of leaning towards it being the TPS. I haven't yet tried to check the TPS function to see if the signal voltage looks smooth across the sweep. Although I haven't actually looked at it, I figured the only way to probe the TPS wire in operation was to pierce the insulation, which I'm not too fond of doing. I sort of figured the connector was sealed and I wouldn't have any luck back-probing it. I guess I could always pull the TPS off and just check the resistance from input to signal line while sweeping the the sensor but wasn't sure how definitive of a check this would be. I did have the bright idea that I could swap TPS between my wife's Cherokee and my truck to see if it fixed the problem but they're not identical.

I was sort of leaning away from it being a dirty IAC because it seemed to me that this problem would be present (at least intermittently) regardless of how exactly the engine was brought back to idle.

 

You can back probe the TPS without piercing the insulation. And what can it hurt to at least clean the TB and IAC per link. Plus, with the TB removed you can check out the inside of the intake.

 

Thanks for the info about being able to check the TPS in place. And good suggestion about taking the time to clean the TB and IAC. Once I take time to do these steps Ill report back on what I find.

 

Reporting back will be much appreciated by all here on DF.

 

failure to idle is most likely a bad IAC or clogged up air port in the well. back side of throttle body.

if not IAC, TPS can also cause idle problems, usually surging but sometimes failure to idle. it can be hard to figure out which one. in your case i'd guess IAC first and just replace it. clean the well and don't forget to put the o-ring on.

 

And that's why I was thinking probably NOT an IAC problem. I probably didn't describe the problem very well to get that point across, but the truck idles fine when it's at idle. When you crank it up, it idles fine. If you roll to a stop from road/hwy speed, it idles fine. It's only when the throttle is closed with the truck essentially not moving that the PCM allows the engine to idle down too low and die. It if DOESN'T actually die when foot is removed completely from throttle, then within a matter of a few seconds it will resume a nice, steady idle.

BTW, I never finished my honey-do list today so haven't had a chance to go work on the truck to check out TPS function or perform the TB cleanout as suggested by zman17