E30 Zone

my mate has got a m20 325i sport and its running lumpy and cuts out on tick over but runs sweet from 3000 rpm and above any body have any idea what it could be

Gummed up or knackered Throttle Position Switch, like every other M20 lumpy idle

daft question i have his car for a week where would i find that switch can they be cleaned thanks mate

It's on the underside of the throttle body, you can't miss it. It pays to drill a small hole, maybe 1 or 2 mm right in the very centre of the switch. It won't do it any harm but it allows the crap to seep out.

Air leaks into the inlet side of things anywhere after the air meter can also cause these problems, aided and abetted by injectors that are 50,000 miles past needing a rebuild.
Remove the air filter assembly, then the large convoluted air hose (checking it for cracks and splits), and you will see the TPS sitting at the lower end of the throttle butterfly shaft.
Pull off the three pin plug, and check for continuity between two of the pins. The meter reading should go to infinity immediately the throttle is moved off of its stop, and become short circuit again as soon as the throttle is released.
The switch fails because oil in the throttle body runs down the shaft and into the switch, from which there is no escape. The cure is to remove the throttle body, complete with switch, and to drill a 1mm hole right in the middle of the BMW roundel on the underside of the switch.
A bit of switch cleaner or isopropyl alcohol into the hole, allow to drain, and the switch should come back to life.

its bolted onto the bottom of the throttle body, 2 screws hold it in place, remove it and give it a good clean with some contact cleaner in the hole.. when u put it back on you have to make sure its set right.
once its bolted on put your ear to the throttle body and very gently open the linkage, you will hear a 'click' the second you move the linkage, if the linkage move a few mm before the click sounds, you need to loosen it off and set it closer. also check your air hoses for cracks/splits. air leaks will make it run lumpy too

re injector cleaning:

perfect for a rainy day