318Ti(M42) stutters/stalls runs unregulary> AFM faulty?

[Niels]

Hi Guys,

Just bought an old 318Ti, which runs very fine at revs but acts like hell stationairy or driving away in first/second. It stutters, has huge revdrops and the stuttering/juddering when driving away really makes it undrivable.
I suspect the AFM myself, so I unconnected the sensor and it does improve greatly, but off course running without afm the car has almost no power left. I don't know what the engine management does when the afm is disconnected: It probably guesses the air flow, but is it still looking at the other measurement values? Ergo: When I disconnect the AFM, Could it be that the system doesn't look at another sensor, f.i lambda value?
However I guess the motor doesn't run on lambda at a cold start? My issue happens both at cold and hot.

So what do you guys think? Should I just replace the AFM or is there a way to mend it? Does it sound like a common problem?

If there is a solution, I guess I would be able to solve it myself.. I have a degree in automotive engineering, but skipped from carburettor-vehicles to electric cars so have almost no experience with fuel injection.

Many thanks in advance for your help!

Regards,

Niels

[DesktopDave]

The car has no other sensors to determine airflow besides the AFM. It will only idle if the AFM is disconnected. Bosch overbuilt those sensors - they do run for an awfully long time. There are a few cases of the internal resistors being worn by the wiper arm. That can be resolved by removing the cover, then bending the arm ever so slightly. The result is that the wiper contacts will sweep over a new surface of the resistors tracks on the internal circuit board. However, I'm not entirely sure your AFM is at fault. Unplugging the AFM should cause the symptoms you're describing.

Sounds more like a vac leak somewhere. Check the rat's nest of hoses under the intake manifold? Any air leaks around the injectors?

If not, I'd be checking a few of the known problems with these engines. First, check all of the sensors. Does the car run better cold? Or does the car stutter whether warm or cold?

If the stutter is temperature based, check out the temp and O2 sensors. If it happens regardless of temperature or when ambient temps are high, check out the coils and coil drivers in the DME. If it's based on RPM, check the crank & cam position sensors.

If the stutter is only at higher RPMs, I'd be sure the fuel system was up to spec first. Run both a bypass pressure test and flow test for best results.

Electric cars? What kind are you working on? The E36 would make a pretty good electric IMHO.