6.2L high idle, any ideas??

[BIOBEV]

My 1988 6.2L Suburban is all of a sudden running at a high idle and I don't know why. It allways had a higher idle when first started but after a couple of minutes when the temp came up it would kick down to a lower idle, now it just stays at the higher idle and doesn't kick down. It seemed to start with the last tank of diesel but I got it from the same station I always buy at and put the same amount of diesel kleen I always do when I fill up. Any ideas what would cause it to idle high and not kick down? Would sure appreciate any opinions.
Thanks

[BIOBEV]

Can someone at least point me in the direction of what makes the truck idle down after a few minutes after a cold start?

[convert2diesel]

You will probaly find that the temp sensor located at the rear of the passenger side head has shorted out. This is supposed to open (and turn off the cold advance and high idle solinoid) at about 135 degrees.

Hope this helps

Bill

[BIOBEV]

Thanks for your reply Bill. Which temp. sensor are you speaking of, the coolant temp sensor or the air intake? Or some other? Your help is appreciated.

[88 K30]

It's a water temperature sensor and it is located at the very rear of the passenger side head on the side of the head. You should be able to see the wires for it coming out of the loom in that location (below the filter). It is hard to get to from above, but can be removed from below fairly easily. But, drain the coolant down pretty far first or you will get wet when removing it...

Do you notice that the engine sounds more "diesel-ish" too? This sensor cuts power to the cold advance and high-idle. When it goes bad, the engine stays idling high and sounds very diesel-ish (cold advance) even after warm up.

[BIOBEV]

88K30 Thankyou! That description sounds exactly right. Now to fix it!
Thanks Again!!

[BIOBEV]

Can you tell me if it will do damage running it with a bad sensor?
Thanks

[wthif]

The advanced timing might be a little hard on the engine, but the high idle wont be. If you are worried about either of them disconnect the green wires on the injection pump. Left (as facing front of truck) is timing advance and right is high idle.