I've got a '89 M3, the car is chipped and has a K&N add on filter. The car has 80 k miles.
When I installed the chip the idle was rougher and the engine became faster to rev up, and slower to rev down. It isn't burning any oil, at least the dipstick says so.I changed spark plugs about 8 k ago but they seem to be in shape (mate brown electrodes and light/medium grey ceramic).
The black smoke only shows up during acceleration
or whith high loads or hill climbing. When the car is reved in neutral(even to red)there is little or no smoke at all. I recently flushed the exhaust system (no cat,no lambda, euro spec)to clean all carbon deposits.
It really seems, rich mixture but what can I do? An exhaust would help? I think the solution has to do something with helping the engine to get more air in order to dilute that extra fuel and get even more power...