Strange idle, whats going on

[Jbevs]

My truck starts great, but as soon as it starts the idle will climb to about 1100 or 1200. Sometimes it even goes as high as close to 1500. My usual cold idle is closer to 950. Goosing it or letting it high idle for some time doesn't do anything. I switched to the back tank ( 3 gal wmo and the rest I don't know what, it is full from the PO) and the idle drops to regular warm idle (650 or 700). This has been going on for a few different times now.

The front tank is ULSD with dieselkleen. I also sounds terrible when idleing high, like it is not getting properly lubricated (valvetrain possibly). I can switch back to the front tank after normal idle is achieved and it will stay at the normal idle. I also only start and stop on the front tank.

Anyone have any idea what's going on here?

Also on a somewhat unrelated note, what size is the oil pressure sender? I am going to cannablize a wrench to get in there but would prefer to know what size before I just start chopping up wrenches trying to get the sucker out.

 

[OLDBULL8]

My guess would be that the throttle cable is sticking at times causing the hi idle, manually make sure the throttle lever is at the idle position when it does that. As the engine warms up there is more complete combustion causing the RPM's to climb.
The wrench size is 9/16" IIRC if the switch has the 3" riser on it. Why are you removing it?

Put you truck in your signature and state the milage. No one has a crystal ball.

 

[Jbevs]

Truck is in my sig. Mileage could be 215000, could be 315000. Gauges are getting put in.

 

[Jbevs]

bump

 

[Agnem]

A stuck timing advance can sometimes cause problems with idle as well. You will need to verify visually that your throttle lever is in the idle position when you are experiencing this problem. The idle set screw is on the left side of the pump when viewed from the front, and should be in contact with the stop. If it is, then check your advance plunger by operating it and noting if there is a change in engine clatter. If that is working OK, then you are having an issue with the govenor internal to the pump, and your options are to either treat it with heavy doses of Howe's diesel treat, or remove the top cover and spray it down with gumout or some type of cleaner. I don't favor this method, as it can accelerate wear in the pump briefly.

 

[Ididriver]

thats exatly what my truck dose when its low on fuel idles stupid high like that till i switch tanks and fill front tank back up