My 83 240 was stalling in hot weather last summer so I used her during the winter months. Now I switched to my 91 240 for this summer and she too is
having the same problem.

Stalls in hot weather, as if she ran out of gas.

She starts up after a short break and then stalls after about 20 minutes.

The main fuel pump is humming and this is what I have done to this point.

I put in a new fuel regulator last week and this did not solve the issue.

This morning I put in a new fuel filter and this did not solve the issue.

The codes I am getting are 1-2-1 (Faulty signal to/from Air Mass Meter)
I put in a AMM I pulled from the salvage yard last night.

and 2-3-2 (Fuel trim (lambda control) too lean or too rich at idle).

I put in a new intank fuel pump 2 years ago.

Today she stalled again and again in hot weather and in backed-up traffic because of an accident (thank you to all the folks that honked at me, I
loved being stuck in 90 degree weather on a busy street).

Then after a short break and a used fuel pump relay swap she got me home.

I am thinking that one of the fuel pumps needs to be replaced next, should
I do the intake or the exterior pump first?

Any and all advice is appreciated.

Joseph in New Mexico