Got our '93 240 5-spd back from lending to our daughter with the Check Engine light shining brightly. She said the light had been on for a while, but the car still seemed to be running all right. Thank you Sweetpea.

The car has about 150K on it and it has been well maintained. The OBD codes were 121 (Fault in signal to/from AMM) and 123 (fault in signal to/from coolant temp sensor). No big deal, I thought. Before I went through the hassle of changing out the FI temp sensor, I first checked it from the ECU connector to make certain it was not a wiring problem. The temp sensor proved to be right on the nuts both hot and cold, so I left it in place.

At start-up the idle is often high (1500 RPM), sometimes normal but always whenever the throttle is blipped, the engine dies. Pressing and releasing the throttle normally does not cause the engine to die.

I then cleaned the mass airflow meter and its connector with no improvement, so I tried a known good AMM - NO change.

The fuel rail pressure is a little low both with and without vacuum (about 29 and 38), but I've seen worse on other cars. Pinching off the return line, pegs the pressure gauge. Manifold vacuum at idle is about 18 inHg. The AMM has good voltage to it and a solid ground. Sometimes the Check Engine light will come on (code 121, again), but it usually clears itself on restart.

Does anyone have any ideas as to what is causing the weird idle and dying out?

Thanks,
Rich