strange throttle problem?

[gandhi]

Just been to a friends, as his E30 325 is playing up, and this is what happened.

When you start it, the motor turns, it catches ignition, sparks up, then the revs fall to about 600, then they bounce up and drop again and again, even cutting out. I thought it was the idle screw, but that doesnt explain what happens when you drive it and try to rev it.

We crept up to a nearby road (at about 1500 rpm, and it ran, but it wasnt smooth revs, coughing now and again). When I put my foot down, the engine cut out (didnt stall), sounded like bogging in a 2 stroke when its too rich. To get any power/revs out of it, you had to tease the throttle pedal down no faster than the rate the revs can increase, otherwise it does this cutting out thing again.

Returned back to his, and again it sounded unhappy at idle, and difficult to drive at slow speeds due to being jerky and me being unable to apply power..

To me (no expert), it sounds like its not getting enough of something, fuel maybe... Fuel line split? pump? could it be the airbox (which is standard)?

Any tips would be welcome

ps, it is very sudden, as the car was used about an hour before for a quick trip, and all was well..

It does have a habit of trying to idle low when cold, revs do tend to drop a bit, the car shudders then the revs pick up again before it stalls.. but never as bad as this..

[OMS]

It sounds like your mass airflow sensor could have gone.. generally when they go the engine tends to hunt i.e. the revs rise and fall as the ECM attempts to set the revs. With it broken when you accelerate the fuel injection system is pushing fuel in based on whatever the mass airflow sensor is telling it, if that's buggered then the wrong amount of fuel is going in, therefore it could be running rich or lean.. Anyway, there's probably a diagnostic tool you could get of e-bay or alternatively look on some of the BMW forums for cheaper ways of diagnosis....

Either way it's worth checking Air, Fuel and Spark

Hope this helps

[The_Burg]

OMS said:

It sounds like your mass airflow sensor could have gone.. generally when they go the engine tends to hunt i.e. the revs rise and fall as the ECM attempts to set the revs. With it broken when you accelerate the fuel injection system is pushing fuel in based on whatever the mass airflow sensor is telling it, if that's buggered then the wrong amount of fuel is going in, therefore it could be running rich or lean.. Anyway, there's probably a diagnostic tool you could get of e-bay or alternatively look on some of the BMW forums for cheaper ways of diagnosis....

Either way it's worth checking Air, Fuel and Spark

Hope this helps

If it s like most cars simply unplug the MAF sensor and see if it improves, thats your fault.
(Engine management will come on but should still run OK, only in limp mode though).