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 before 0, but the engine is still running and you can feel a very
slight vibration or rough noise, very hard to feel or hear Must turn
off A/c and radio. 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 for
5 min breaks. 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? Is it expensive to fix?
Is the engion oil sludge?

Thanks