Fueling answer please.
Moderator: martauto
If there is an induction air leak is it right to assume the additional air will trick the ECU in injecting more fuel, therefore this over-fueling will show on the spark plugs? (I know assuming anything is foolish but...) 1990 325i.
No this is incorrect. If there is an air leak in the intake system, it will almost certainly be after the air flow meter (AFM), therefore the ecu will not know that there is extra air entering the system and the engine will run lean.