Detroit idle problem......

Did you check the ECM for error codes?

 

Do diesels have an idle air control valve???

If so that would be my bet, either that or the the throttle body is dirty or shot... Sorry, I don't know that much about diesel engines.

 

diesels after '91 Have ECM's that are the brains of the engine. The problem could be a simple error code.

 

If an electronic controlled truck starts playing on the first stop should be the check for error codes. those little codes can save hours of hunting for issues..

 

In the old days, fast idling could mean an air leak into the fuel system at the filter.

 

I'd rather go back to the mechanical engines but the "Nanny State" says otherwise....

 

On my truck, if you turn the key on and hold the cruise set switch down on coast, the check engine light will flash out any codes stored in the ecm. Not sure if Detroit will work the same way

 

I would bet on the throttle position sensor under the fuel pedal. There is a lot of dirt and moisture from wet feet around those things.

They usually don't set a code unless they are totally out. You can have the output read with the right equipment. The cost for a replacement is sometimes cheaper than getting it checked.