High idle

[Big_Dave]

After checking under the hood (motor warmed up already), I kicked my truck up to about 900 rpm's this morning while I finished my per-trip.

As I got around back of the trailer, the high idle kicked off and it returned to normal 'low idle'. :wtf:

Never had that happen before.

3406E Cat.

[Capt._Chaos]

Might be the switch in your dash behind the aie valves that returns the engine to its low idle speed when you release the tractor brakes. It can act up intermittently (happened on my truck once).

If you have a defective coolant level sensor (bad connection), it will do that occasionally

[nitestar]

Dave

One thing that may cause it is an air compressor using oil and the dryer is soaked and the oil is getting to some of the valves on the truck.

I had something like that happen to me. The leveling valve for my suspension was malfunctioning and the valve was soaked with oil. Oil traveled from the compressor through the system to the very back of the truck. kind of scary to think about. oil contamination in every thing.
very hard to clean up.
Just a thought.