E30 Zone

what are all the common causes for the m40 running lumpy on idle

im no extert...

but get some carb cleaner, clean all the throttle housing and ajust it, and inlet thing inside the big rubber boot (the 2 flap type things that the throttle works) , clean the icv , and air filter, and check all the hoses and things like that

recently done that on myc ar and its running great

will do cheers sounds better than replacing parts

dizzy cap and leads can break down. i have a very very low milage set for sale, you just need to buy a rotor arm.

made a huge difference to my car.

also, the intake boot can split and cause an air leak which doesnt help the idle

whip off the rocker cover cap when the engine is on idle if it doesn't change lumpyness check for air leaks.

pm sent

I had this problem, I did all of the things suggested, and replaced the breather pipe to the idle control valve, adjusted the idle stop screw, and it's working fine.

E30's DO NOT HAVE AN IDLE STOP SCREW! Leave this adjustment alone.
It was set correctly at the factory, and unless its already been got at, is still set correctly.
The same applies to the adjustment on the AFM.
If adjusting either of these results in improvements, you are just masking another fault, and making that original fault very difficult to find.