OK, folks I hope you can help, I am new to this forum but have always had great luck trouble shooting other issues on forums. Anyway I have a 01 2500 that I bought used, I had a plow put on when I bought it so it was never plowed before. I have already had the tranny go and rebuilt. About a week ago I noticed the truck leaking something. The ground was wet so I was unable to tell what it really was (oil, tranny fluid, power steering fluid, etc). I went home checked all the fluids and only the power steering was low, topped it off and have not noticed any leaks lately. In the last week the truck has been ideling funny, I have a remote starter on it and always walk by when the engine is running and have noticed a difference. Not rough or anything that has affected performance but just different. Today I am driving, with the plow on, and merging onto a highway, getting up to 55 I let off the gas and the truck shuts off. Pulled over shutdown everything and the truck restarted right away. Oil pressure was good, coolant temp was fine and battery level was fine. Drove to work, another 25 min, and nothing else. Any ideas? I have not had any major issues, besides the tranny, with this truck (oh yeah and the doors rusting out) and would like to stay ahead of one if that is were I am heading. I just have a bad felling that something major is about to go!

I would appreciate any input.

Thanks
Steve

 

That doesn't sound like a tranny problem.
What is idle 'different'?

 

My first thought is maybe the IAC valve is sticking and when you had let off the gas, the A/F mixture changed too suddenly and too far off from where it should have been, and caused it to stall. This could also explain the different idle. On the same frame of mind would be the TPS being out of whack causing the same conditions.

 

Trying to describe and idle is somewhat difficult, lets say you imagine an engine idling normal, purring like a kitten. There is a constant cycle to it now, with a quick low in it. Like a sine wave pulse lets say.

Ok teach me something. I have not worked on this truck or late model engines much. What is an IAC valve? The throttle position sensor is a good thought. Do you believe these items are something I could test quickly? Or do you think I would have to bring it to a mechanic? I just hate replacing parts before I know what it is. I also hate paying someone to do work I can do.

 

You may want to check for any codes stored in the PCM. If you have an Autozone close to you, they usually will check it on a hand held scanner for free and give you a readout on any codes present in the PCM. That would be a good place to start.

IAC valve - Idle Air Control valve.

 

I have a code reader, I think. I have a handheld code reader for the OBD port under the dash but the check engine light is not on. Wouldn't it be on if there was something wrong?

 

This sine wave action... is this after the truck is warmed up? If it is it could be the fan clutch kicking in and out.

Ok, if it were me I would tackle these things in this order.

1. check tps (not likely your problem) I believe there are three connectors on the tps plug. Take a volt meter and put the red spike into the center wire/connector (while the connector is still attached to the sensor. There is enough room where the wire enters the connector to stick the spike in and will hit the metal contact. (you'll see what I mean). Attach the black lead to a ground. Have a friend hop in the drivers seat and turn the key two clicks forward to when you hear the fuel pump kick on. check the beginning voltage (I forget) and have your friend slowly push on the pedal. if the voltage keeps rising as the pedal is pushed further down (meaning no dips in voltage) the tps is still good.

2. If the tps is found faulty, replace. (again not likely the cause of your problem but it was mentioned above so I figured I would tell you how to test.

3. Reset the computer, there might have been some slight fluke for some reason and this will give the computer a chance to relearn everything. It takes 50 miles or so for the computer to return back normal operation. If the idle problem still comes back, move to step 4.

4. as ron333 said, the IAC is probably the culpret. To stay on the cheap side, your next thing you can do is to remove the Throttle body and remove the sensors and clean. Carbon buildup can sometimes cause wierd things to happen. If the cleaning doesn't help, replace the IAC motor.

Reference this DIY https://dodgeforum.com/forum/2nd-gen...ttle-body.html

5. My next guess would be a vaccum leak. While you have the TB off, take a look at the plenum (if both IAC and TPS replacement do not fix the problem) See if there is pooling oil etc.


Let us know what happens. Good Luck!

 

TPS is on drivers side of TB. IAC is on the back. search this site for a million posts about them. in general the IAC is responsible for the idle, and the TPS tells the computer where your foot is in the gas. frankly, its hard to be sure which is malfunctioning, because they work together. i've been fooled more than once.

they cost about $40-50 each. you can replace them both in 15 minutes for less money than you'll have to pay someone to even look at it. if that's not it, then keep your old ones for spares.

a lot of people talk about cleaning them. that's never worked for me. when they went bad, they just went bad, they weren't dirty.

edit. if there's a code set, the cel will be on. you can read the codes by doing the ignition key on-off-on-off-on. last time my TPS went bad it started acting crazy and it took a week or so of craziness before i finally got a code P0123, tps voltage.

 

I appreciate all the feedback and I will check this stuff this weekend if i have the truck. I was out last night and parked the truck after about 45min to 1hr I went back to the truck and with the wet ground it looked like an oil slick was under my truck. I drove home check the tranny fluid and level was still fine but almost had a burnt smell to it. Checked the engine oil and I was down 2.5 qrts. I topped it off last night and threw a piece of cardboard under it to see if it leaked, it did. Not a lot but a little puddle. Drove it to work this morning and I could smell oil burning off, like after I change my oil and spill a little. I am trying to make an appointment for someone to look at it today. I will let you know what happens. I fell like the truck shutting down on the highway might have been just a weird coincidence.

Thanks for the help,

Steve