I've been reviewing the posts regarding lumpy/rough/etatic idle with the M50 / M52 engines. I have a 1991 e36 320 with the M50(TU) engine which exhibits rough idle when cold, warm and hot. The idle does not hunt (revolutions are static at around 800RPM) but feels rough as though the engine is missfiring. There is also a relatively strong smell of fuel on idle.
The car has a LongLife stainless exhaust from the downpipe back. I also have a K&N induction filter fitted.
I have replaced the following components:
Coil packs (second hand BOSCH coil packs)
Lambda sensor (new four wire sensor)
Air filter for K&N induction filter
Exhaust for straight through stainless steel from downpipe back
Spark plugs (NGK)
Complete oil change
When I first attempted to change the lambda sensor I had the wrong type (Titania type four wire type with black, yellow, red and white wires) which did not match with the wiring under the car. I had this changed for the correct type (Zirconia type four wire with black, grey and two white wires). I beleive that the type of lambda sensor used changed in 1992; 1990 to 1992 a Zirconia type was used, 1992 onwards a Titania type was in use.
However after replacing the lambda sensor the idle appears to have become slightly rougher. However I am not sure if this is because the lambda is incorrect (the wiring matches and my local motor factors who are usually excellent tell me this is the correct lambda sensor for the car) or if now the lambda is functioning correctly it is amplifying a problem elsewhere.
The coil packs have all (6) been replaced with second hand BOSCH components supplied by Quarry Motorsports. The coil packs all appear to be visually ok.
Spark plugs have been replaced with the correct NGK replacements.
I am at a loss as to what is causing the rough/lumpy idle. So my questions are:
Could it be the ICV? I would be supprised as this wouldn't cause a "missfire" like symptom. If so where is it and how do you clean it?
I have read that the oil used on K&N filters can cause the MAF hotwire to become coated in film that can cause this issue. Is this the case? If so how do you clean the MAF?
Could the Crank Case Vent Valve cause rough idle? If so how do you clean it out and where is it located?
Could the lambda be incorrect? If so how?
Any issues surrounding the crank sensor?
Any issues surrounding the ECU? (I'm thinking about having this remapped/chipped anyway)
Any other ideas?
I am supprised to be having this issue on a BMW. I used to own RX7s and was used to all sorts of idling and air/fuel ratio issues. The symptoms seem to indicate either overfueling or poor spark. However I am at a loss as to what could be causing this having replaced the obvious components.