My 1989 240 (non turbo) quit running this summer in 105 degree heat. It was like it was running out of gas. The tank was full, it has a new fuel pump in the tank and a new fuel filter. We let the car sit for several hours to cool off. It started and we drove 3 miles before it stopped again. I let it sit again and drove 1/2 mile home. It popped two codes.
121 - Fault in signal to/from air mass meter.
231-fuel system compensation for rich or lean mixture at cruise.

I waited 2 days for the weather to cool off, then drove it 9 miles around the neighborhood -- it ran fine. I have been afraid to drive it.

My buddies tell me to change the "air mass meter". I changed it years ago while chasing another problem (the original was not bad).

The car has 145,000 miles, we purchased the car new.

They tell me a air mass meter is about $200. I do not mind spending the money if that is the problem. They tell me if it quits again to disconnect the electrical connection at the AMM-- it should start and run (poorly - but it will run). I have not been able to duplicate the problem.

What would you do ?????????????????????
Thanks for your in put. Don

 

It may be your air mass meter. One thing that causes failure of the AMM is the thermostat within the air filter box. There is a large metal tube that runs from the exhaust manifold to the air filter box. Inside the air filter box is a thermostat that opens/closes a valve that lets in warm air from the exhaust manifold. This valve is there to let pre-heated air in when it is cold out. When the valve fails, it lets in warm air all the time and in the hot summer, it can fry your AMM. Many people remove the metal pipe that runs from the exhaust manifold to the air box or permanently close the flap in the air box.

To test your AMM, the best is to swap in a known working AMM and test drive it to see if it throws any codes. I would start by fixing the air box issues, reset the codes and drive it for 30 or more miles to see if it re-throws the codes.

 

...or...the codes could be old codes that were never removed from the system and it is your fuel pump relay intermittently failing.

 

+1 fuel pump relay