1997 Pete 379 with N14 - Idles out of Control

I bought a 1997 Peterbilt 379 with a Cummins N14 a few weeks ago. The truck has Cruise Control & Cummins Celect. When I put the truck in Neutral, the Idle races out of control (to Wide Open!) until I punch the accelerator pedal. It idles down, then it idles back up out of control again and I have to hit the pedal again. This started 2 days ago, which was right after I removed the Instrument Panel to install chrome switch covers. I removed the Cruise Control & Cummins Celect switches and then reinstalled them. Could this be the problem? Could some wires be touching each other or grounding out? I can't leave the truck running while I hook up trailers or open gates because I am scared that I will blow the engine. I will check the wires on the switches in the morning.

 

Nothing on the shifter - only on the Dash/Instrument Panel. Just a 10 Speed Eaton Fuller. It seems awful coincidental that this started after I removed the switches. I got in late tonight, so I will troubleshoot it first thing in the morning.

 

I removed the Instrument Panel this morning and found the wire harness unplugged from the Cummins Celect Diagnostics Switch. I plugged it back in and had no troubles all day. Then at the end of the day It started idling out of control again. I checked the wire harness plug again when I got home and everything looked good. Maybe the switch is going bad or I damaged it messing with it the other day. I will just keep watching it.

PS. I still don't know how the Cummins Celect works? When you put the switch in Diagnostic mode, should something flash in the dash?

 

Problem Solved. It was a bad ECM. Changed out the ECM with a test ECM at a shop and the engine smoothed out perfectly (there has been a miss in it since I bought it last month). I found a used ECM for $600 plus $100 to program it and $190 for the shop to remove it, reinstall it and check all of the programing. A new ECM from Peterbilt Dealer was $2,500 plus $500 to program & install. The truck hasn't had the issue again and it's been a week.

 

Well, it is starting to scew up again. Not the idling out of control, but the Check Engine Light starts intermidently coming on after about half a day of running - only when slowing down to an idle. The #4 Injector is throwing an error code (I had the computer codes read the other day). I think that it may be a bad wire going into the ECM.