01 Dodge Dakota – engine idle problem

01 Dodge Dakota 4.7l v8 (167k miles) has an engine idle problem. The idle is fine when cold, however once the engine has warmed up, I experience a low engine idle problem. Normal idle is around 650 for the truck, the low idle problem is dropping the idle to 500. It doesn’t kill the engine when this happens, but you can hear it’s right on the edge of doing so. It only happens in gear. If the truck is in park engine idle is fine regardless of engine temperature. I normally notice the low idle after the engine is warmed up (never on a cold engine) and when I pull up to a stop light. However, it does NOT happen 100% of the time these conditions are met, I guess probably 80% of the time I pull up to a stop light and the engine is warm will the idle drop. I’ve read through Eric’s idle problems page but need more direction. TPS was recently replaced months ago for a different problem. And as a guess, I slapped an IAC valve on it a couple weeks ago, but that didn’t fix it either.

Any suggestions would be much appreciated.

Thanks