Volvo: 91 Volvo 940 Turbo would die at low RPMs now will not start, mass air meter, crank sensor

Question
Ray,

I've had some on-going problems with my 940T for the past few months. The battery is new with clean connectors. Alternator voltage is fine. Cap, rotor, wires and plugs are all new. Spark has been verified at every point from the coil to the plugs. The secondary fuel filter, crank sensor, fuel injector resistor unit and fuel pump relay are all new. The secondary pump comes on when the key is in auxillary. No lambda sensor lights or any other lights. Fuses are fine, checked with a meter. The FP relay was the last installed. Starting was fine for awhile but during the heat of the day it would die at idle with all the lights on like it was not getting exhaust flow or not getting air. If I throttled it above 1000rpms the engine would stay running but if I let it idle it would run rough for a few seconds then die. At night or early morning it ran fine. It has not started since the last time I let it idle on its own and died. I dropped the catalytic converter and tried to crank but still wouldn't fire. The last time it was running it didn't have the symptoms of a clogged primary fuel filter. Power was good through the entire RPM range at all loads. I have a feeling the cat might resolve the low rpm problem but the latest starting problem has got me stumped. Mass Air Meter? Cold Start Valve?

Thanks.

Mark

Answer
Mark,
I would start by reading any codes and if there are any for fuel trim or the Air Mass meter I would look for a replacement AMM. Have you checked for "pulses" at the injectors when you crank it over? If no pulse possibly the powerstage or control unit.