My wifes 1989 240 non turbo has had a new O-2 sensor,new air control pump, fresh plugs, air filter & I've checked for vacuume leaks and cleaned the throtle body.
The idle is constantly up and down by about 200 RPM. It also starts hard when cold and often stalls on the first & second try. Runs fine other wise.

Would a faulty temerature sensor cause an iratic idle even when the engine is warm??

Have you tried unplugging the AMM? (Air Mass Meter)
If the output from the AMM is incorrect the injection system may oscillate, and idle may surge up and down.
Remove connector from AMM and try to start the car. If the car idles fine in "limp home"-mode the AMM/connector/ground may be the problem.
Search for AMM to find more details.

My AMM (016) were measuring 1.3V instead of 1.4V while idling, but it took me nearly a year to hunt down somebody with the same car to swap parts with. After I had tried borrowing an OK AMM I went ahead and bought a new on a trip to Sweden (about $375). Now it runs smooth again...


--
Frode P. Bergsager
240GL '89 230F
Norway

How did you check for vac leaks? Did you spritz WD-40 at things when the engine was doing this? Mac

if RPM is Hopping up & down for few hundred, then ICV maybe unable to do it's job & ECU is kicking in to fix the problem. Recheck the air leaks, if everything is OK, I would take the ICV out and clean or test the ICV.

Try checking these:
1. Operation of the throttle position switch
2. Clean out the idle control motor
3. Set the throttle linkage exactly by the book. Too much to do to list all the steps here but the throttle plate must be exactly centered in the venturi, the shaft positioned right, the linkage set with a feeler guage, and the throttle position switch set to operate at the proper position.
4. Clean and grease the connectors to the switch and the idle motor.

While it hasn't happened to me (yet), I'd think the engine temp sensor, the one back under no. 3 intake runner, could be a cause of the hard starting. My manual says to check the sensor, the throttle position switch, sensor and ignition wires and connections, and the engine speed sensor.

The B230 in my 940 had a hunting idle. I finally cleared it up after cleaning and greasing the electrical connectors and setting the throttle plate and switch.