Last spring my 91 740 started having intermittent fuel problems that got worse. The car would not rev well over initially 4000 rpms and then later 3000 rpms. In the process of chasing this I changed, the plugs, cap, rotor, wires, radio suppression relays, ignition module, fuel pressure regulator, all turbo hoses, AMM, air filter, fuel filter, vacuum lines and I think a few other things that I have forgotten about.

I brought the car to two mechanics; both said they saw nothing wrong with it.

Eventually I noticed that the car would act up, then if I shut it off, and turned it on it would be fine. while a mechanic told me it was likely not the cause, i changed the original ECU (i want to say it was a 951 or an 851, which ever one is the original for a 91 turbo 5 speed) and replaced it with a 937. I then drove the car for 10,000 miles and 8 months with no problems.

With the cold weather in New England here the car has again started acting up. Most of the time I drive it is fine, but now lately sometimes when I turn it on, it bogs down at around 3500 RPMS and will then buck and hesitate, it does not die it just feels like its getting no gas. I brought it to a new mechanic that seems decent and works mainly on older European cars and when I dropped it off it was acting up and they witnessed the problem and drove the car while it was doing this. Then with out doing anything, when they started it up again the car has been fine and revs right up to the redline.

Both fuel pumps seem to work fine and my understanding is that they do not fail intermittently, also the level of the gas tank does not seem to effect the problem.

Do the 937 ecu's crap out like the earlier ecu's as well? The FAQ seems to mention some issues with failing causing the pre-pump to not work, and a deterioration of the hybrid chip. Is there anything else this could be besides a failing ECU and if it is likely the ECU does it pay to go with a rebuilt unit and if so from where?

Is there a way to test the ECU? In the spring when this last happened I talked to a Volvo dealer about it and they assured me that ECU could not fail intermittently.

I am pretty sure its not the AMM as the car throws no codes when it acts up, it seems to think that it is working correctly.

In two weeks I have to start driving 100 miles a day with this car. Any thoughts would be appreciated.