idle problems -when warmed up

[beau55]

My 93 idles perfectly when cold, however when it's fully warmed up, the idle seems to slow and the truck shakes. It's even worse when the AC is on. If I use my foot to raise the idle just a bit, it smooths out but I think that would be to fast to permanently set it, especially since I have an automatic....
Could this be related to the KSB?

[Begle1]

An RPM drop once warm is a common gradual symptom of a wearing out injection pump.

The fix in that case is to increase the idle speed using the low speed idle screw to the point that it doesn't drop too low once it's warm.

Do you have a tach to know exactly how many RPM's it's dropping and what it's idling at to begin with?

[beau55]

The engine has 187,000 miles on it, and runs perfectly otherwise.The pump is a rebuilt unit, and is modified for performance, and has only about 30k miles on it.
I don't know the idle speed - no tach. However, I would say that the engine is idling about perfectly when cold or cool, even with the ac on. But when fully warmed up, it drops too much...the truck shakes and it sounds...scary when in gear, with the ac on.

If I raised the idle speed, it would be too high (when the engine was cool) for the automatic transmission....