triplecore

I have 98 Lexus ES300 with 77,000 miles. Here is my problem. The car starts and cranks fine and runs fine usually. But sometime right after I start the car and it is still in park the RPM gauge drops to the last line, but the engine is still running and you can feel a very slight vibration or rough noise, very hard to feel or hear. When you put it into gear say D the car doesn't roll forward until you press the gas. Usually with automatics the car rolls forward a bit even with out pressing the gas. If I step on the throttle a few times or just ingonore it and drive say for 30 seconds like leaving a parking lot. Then the idle goes back to normal around 1 or the line right below 1 and the car is fine. It so far has only happend right after I drive and try to restart the engine, like quick stops. It has never happend yet when the car has sat for a while right before starting it like in the morning.

Does anyone know what is causing this problem?

Thanks

Pheonix

1) Clean the IAC valve - for that matter the entire upper intake manifold, and everything that connects to it - by hand.
2) check for vacuum leaks.

triplecore

Is this expensive to do? This isnt a sign of engine oil sludge is it?

Pheonix

No. You need some kind of brush, and some kind of cleaner. WD-40, Deep Creep, TriFlow etc.
The best thing to do is take the entire manifold off & clean it. In which case you *normally* need 14, 12 & 10mm sockets, and an allen wrench.

Search for IAC valve on here. There should be directions on how to do it.