Possible issue with CAS in 90 Q

[mattd1979]

I am having problems with my car stumbling when accelerating. It starts to break up at around 4000rpm and doesn't let loose until 6500rpm and then takes off until 6900. Originally what happened was my MAF went bad. While I was connected to the car with my computer, I noticed that the maf voltage was reading .2v throughout the rpm range and the o2 sensors were both reading lean. I whacked the top of the sensor and then the car began stumbling and I noticed that the voltage jumped to 5v through out the rpm and now both o2 sensors were reading a steady rich. I had a back up MAF that I connected and it cleared up enough to be able to drive but it would stumble when accelerating, especially when floored. I figured that the back up MAF had it's own problems. So I ended up ordering a replacement. When it arrived, I installed it and found the car was doing the same thing. A friend of the family has a 91 Q that I ended up swapping the MAF onto his car and it ran just fine. Even during WOT. I also swapped my ECU into his car and it still ran just as good. I disconnected both connections to the TPS to see if it made a difference which it didn't. The only noticeable change is when I disconnect the MAF connector, the engine will smooth out and will have good power up to the fail safe 2000rpm. It will even brake loose the tires at part throttle. I ended up testing the harness to see if there was a short and there was none. All 3 pins read at 000 ohms when testing from the MAF connector to the ECU connector when both are disconnected.

Anybody else run into this situation? I figured that I have run into every problem on this car and then a new one pops up. The strange thing is that the power comes back and the stumbling stops when disconnecting the MAF but I have ruled out the MAF, TPS, and o2 sensors. I know that if the fuel pump was bad then how could the stumbling clear up and power return? I did test the fuel pressure back when the original MAF went bad and found that it was putting out almost 50 PSI when at WOT.

Matt

[mattd1979]

I just finished testing the CAS and it appears to be fine. No surprise since the car runs just fine with the MAF unplugged until I rev to 2000rpm. I can't seem to figure this out. This is my only way to get around and don't know what else to due. You can here the car stumbling at idle but smooths out completely once disconnected. Have I missed anything?

[mattd1979]

Well just so everyone knows, I believe I have solved the problem. My fuel filter disintegrated and was plugging up the fuel line. I also discovered that after replacing the MAF with a 3rd party new one, The power was reduced as if a volume knob was turned down. As you would get past 4000 rpm, the engine power would fall off before it would shift. If a normal person was driving this from the start that had no idea of what this car produces as far as power, they wouldn't have noticed anything. I since put my backup MAF back on and the car woke up. I suppose I will be saving my money up for a new OEM one down the road and also replace the fuel pressure regulator.