E46 328i Throttle Box problem?

[zelbo]

I've got a 1999 328ise which has developed a misfiring and loss of power when the accelerator is depressed, the tickover seems OK. The eml and warning lights have all come up, I've had it checked on a diagnostic machine and been told that the fault codes relate to the throttle box. Has anyone had this problem, is it easy to fix or a specialist job? Any help would be appreciated.

[andy665]

By throttle box I'm presuming you mean the Mass Airflow Sensor (MAF) - just unplug it - if it appears to run more normally then thats your problem, a 10 minute job to replace but based on experience I'd always get an OE replacement - pattern MAFS never seem to last

[zelbo]

Thanks Andy, the mechanic who checked the faults said it was to do with the electronics on the accesllerator/throttle, do you think that is the MAS? I don't know very much about the engine so not sure where that is.

[m444ttb]

Those are the exact symptoms my 328 (an e36) had when the MAF failed. As posted above simply unplug it and see if the symptoms are largely gone.

I replaced it with a known 2nd hand MAF as a mate was working at a BMW breaker at the time.

[TheEnd]

You'll need to get those codes checked again and find out what they really are, as there isn't a throttle box.

There is a Pedal position sensor, and a throttle position sensor, and if there is a problem in them somewhere, the throttle might not respond to the pedal.

[zelbo]

Thanks very much for all the help and advice, I've done some more investigating and the symptoms certainly seem to be pointing towards the MAF. Where abouts is it to unplug it to check if this is what the problem is?

[phelix]

TheEnd said:

You'll need to get those codes checked again and find out what they really are, as there isn't a throttle box.

There is a Pedal position sensor, and a throttle position sensor, and if there is a problem in them somewhere, the throttle might not respond to the pedal.

Actually, there is a throttle box, or something similar. The M52TU has a throttle cable but also a servo motor to control the throttle butterfly. It serves two purposes - it's used for the cruise control and it allows the throttle to close slower for emissions purposes. Worth just resetting the error codes and seeing if they return.

All that said disconnecting the MAF and seeing what happens won't do any harm.

[TheEnd]

What there is, is an electronic throttle, the MDK, which may be the cause of the problem.

That and the throttle pedal have 2 position sensors each, and both sensors on the pedal and the throttle need to match exactly otherwise it will realise that a sensor is wrong.

If you disconnect the MAF, you'll also end up with a MAF fault code the next time it is tested.
It uses the MAF as a 3rd virtual throttle position sensor by knowing what air should be passing through so if one throttle position sensor goes bad, it looks at the airflow, and will then figure out which one of the sensors if telling the truth, and which one is the busted one.