After spending loads of money last year on a stainless downpipe with sports cat to get my scoob thro' the mOT, it has now failed on %CO on fast idle test (1st and 2nd).

It is reading .39 and .40% against a limit of .30

Ever since last year have run on super unleaded and now optimax. Fitted 57i last week.

Anyone got any clues? MOT man said take it for a thrash and then come back - which I'll do tomorrow.

Car is a 93 WRX (import) - should this be subject to other limits than a UK model?

Do a search on here for MOT and imports, your car should not have to pass the emissions test for a 'catted' vehicle.

I'm surprised you car failed with a sports cat in the D/P, my car car passed its first MOT yesterday with a std UK center pipe and a decat d/p.

Did the tester perform the 'catalser conditioning step' when your car initially failed the fast idle test?

Andrew...

Whooopeeeee - an ECU reset and a 15 mile cruise along the motorway gets me a pass - I'm happy now