Audi backfire between gears - Mole

My '93 A80 2.0 backfires between the gears (usually 1st-2nd). It's more of a loud f*** than a proper backfire but it's annoying. Car has just had new cat and lambda sensor (it did it before I changed 'em) and sailed through an MOT test today. Plugs are whitish grey which used to mean a lean mixture (not sure if it's still relevant on this closed-loop nonsense).

TIA

Brian
Audi backfire between gears - Peter D
use a small bore plastic pipe and listen round the madafold gaskets and injectors for a leak sucking in air, this could be the sourse of your F***. Check the ECU fault codes just in case but I suspect induction of O2. Regards Peter