After starting, idle speed is low. So low that it stalls when you put the car in gear. After a couple of minutes it slowly increases.
I've cleaned throttle body, cleaned idle speed motor, and tuned it up. The diagnostic system shows no codes.
What am I missing?

Frank

I wish we could share our problems, my 91 240 idle is too high (950 rpm). Initially, my idle speed was low. Like yours, it began to occasionally stall. After cleaning throttle body (TB) and adjusting the mechanical stop and throttle position switch (TPS), my idle speed was 950 rpm. I have become very familiar with the idle speed control system, but am not yet sure exactly what my problem is. I suspect it is the Idle Air Control Valve (IAC) located just below the intake manifold. Mine stays wide open and (i suspect) allows TOO MUCH air to bypass the closed throttle valve during idle conditions; hence my idle rpm is too high.

In your case, I suspect your IAC is not opening, or not opening enough to allow enough air to bypass the closed throttle valve. If you remove the IAC, it is easy to clean (can get gunked up and stuck). Also, you can bench test the IAC. You should read 8 ohms across the terminals of the IAC motor.

I would check the engine temperature sensor and the O2 sensor; both of them have an input to the ECM which influence the idle speed.

I cleaned and checked IAC motor- 8 ohms.

Where is O2 sensor and how do I check it?

Where is engine temp sensor and how do I check it?

Thanks for the input.

Frank

O2 sensor should be screwed into the cat (if your a pet lover, no offense, cat stands for catalytic convertor).

the temp sensor should be screwed into the block on the drivers side, not far from the IAC

Do you have a Haynes or Bentley manual. THey are helpful in diagnosing, testing the sensors.

I have a Haynes manual, and will try to use that.

Thanks, Frank

you can easily measure the coolant temperature resistance if you have an ohmeter. Remember, it is a thermister, meaning it's resistance will increase as the temperature decreases and it's resistance will decrease as the temp increases.

So, it's resistance will vary depending on the temp of the engine. The resistance readings are in the manual, i do not have mine with me at the moment.

There are also some resistance readings for the O2 sensor, if my memory serves me well

good luck