Car cutting out when put into drive or reverse

hi

forgetting my previous posts and putting all these symptons together

I have a series 1 SWB TT Auto

test drove it and all was fine

came back out an hour later DRIVES PERFECT

but the revs go a bit up and down on tickover

it smells a bit of petrol round the engine bay SOMETIMES nowhere else cant see any leaks

Drives with great performance

exhausts seem a bit sooty considering ive done only about 5 miles

and heres the one put into drive or reverse and most of the times its wanted to cut out on me didnt the first few times

what shall i do for the ecu check as Id like to sort on the weekend

ta chris