Maf Voltage issue

[200kclub]

The car is an early model 325e and it has a new MAF sensor. Runs and idles great when MAF is unplugged, but as soon as its plugged in the car runs like shit, the same way as if the MAF was broken. Obviously this means bad voltage to the ECU. How do I pinpoint the problem further?

Do I Need a new DME unit?

[thejlevie]

Actually that isn't the most obvious meaning of the engine idling better with the AFM disconnected. The most likely reason the engine idles better then is intake leaks. When the AFM is connected the DME thinks it knows how much air is entering the engine and computes fuel based on that, engine speed, and temperature. If the engine is in closed loop the DME also uses O2 sensor data. But if there are intake leaks more air than is being measured is entering the engine and the calculated fuel delivery is insufficient. With the AFM disconnected the DME uses default data that is based on engine speed and temperature.

[200kclub]

Actually that isn't the most obvious meaning of the engine idling better with the AFM disconnected. The most likely reason the engine idles better then is intake leaks. When the AFM is connected the DME thinks it knows how much air is entering the engine and computes fuel based on that, engine speed, and temperature. If the engine is in closed loop the DME also uses O2 sensor data. But if there are intake leaks more air than is being measured is entering the engine and the calculated fuel delivery is insufficient. With the AFM disconnected the DME uses default data that is based on engine speed and temperature.

Intake leak before or after the maf housing?

[Gregs///M]

You need to figure out if your car actually has a MAF or AFM. They are completely different. A MAF was never equipped in the E30, only with after market installations. The original equipment is an air flow meter (AFM.)

It will show a 0-5V DC voltage that increase exponentially as the internal flap opens. You can do a minimal test with a meter but to be really conclusive, you must measure voltage over time using an oscilloscope.

IN my opinion, and i rebuilt well over 100 AFM's, any original AFM never rebuilt, is bad.

Is that the cause of your problems? not necessarily. Many factors can contribute to your running issue as Jlevie mentioned.

[thejlevie]

Intake leak before or after the maf housing?

After the AFM. A leak there allows unmetered air into the intake.