Fast idle while warm or cold

[1994Diesel]

The truck that is idling fast is the '93 in my sig. This truck is actually my grandfathers, and he loaned it to my uncle for the time being. So the situation is i am the only one that EVER maintains this truck, i try to do what i can when its around( sometime i cant get my hands on it for months at a time).

Just recently my uncle swung by with the truck and it has a fast idle, at about 1200rpm, he says its like that all the time now, even when warmed up. Of course i couldn't get a look at it because he needed to be some where, but it sounded a little funny when he was pulling away down the street. I couldn't hear any timing advance but there seems to be some increased mechanical noise since i heard/ saw it last.

What could possibly cause this? Obviously a malfunctioning fast idle solenoid could be the culprit. Is there anything else that can cause fast idling? Injection Pump failure?

Pump failure doesnt sound right though, because it is easy starting.

Thanks guys, any help is appreciated!

 

[franklin2]

Check to see if the temp sensor has gone bad. It's what activates the fast idle/advance. It's located on the front passenger side of the engine, down in behind the alternator. If you unplug the sensor and the problem goes away, then the sensor is bad.

 

[65sixbanger]

Unplug the sensor and run a manual switch...

 

[Agnem]

It is possible for the pump to have an advance problem, or a sticking govenor assembly. So basically, you need to rule out the external electrical or mechanical influences, and then know it is a bad injection pump. Either that, or someone put a new electric fuel pump on it with a high output presure, in which case he should be complaining about other things.