I'm writing this for a friend who has a 1998 A4 (I've got a more recent A6) - the other day his car died at at stop light, restarted fine, but the idle wandered +/- 400 RPM (600-1000).

We checked his car and it's thrown these two codes:

P0411 - Secondary Air Injection System Incorrect Flow Detected

P1136 - Fuel Trim: Bank 1 (Add): System too Lean

Any ideas what might be causing these? I suggested a vacuum leak or maybe a MAF.

 

in my amateur opinion, it definitely sounds like an air/vacuum leak. do a smoke test of some sort.

 

My friend took it to an independent shop - Ended up being a Mass Air Flow sensor for the Fuel Trim. The 2nd air flow pump was bad too. Thanks for your suggestion - that was my guess too.

 

I'm often wrong. I really hope people double check because if they take my advice and pay needless money I feel bad.

Anyway, glad it's fixed!