markpaul

I've recently purchased a '91 S4 (Amethyst Metallic with black leather and magenta interior trim) which has had deferred maintenance because the previous owner ran out of $ after spending $7K rebuilding the auto box not long after buying the car. It needs cam belt/water pump, rocker cover gasket replaced, air con fixed & many smaller jobs. The list keeps growing but I knew there'd be plenty to do & got it for a good price because of this. There are two things I really need some ideas about - firstly there's a loud buzzing the begins behind the centre dash air vents when the car starts. It slowly fades but is always there albeit quietly after a few minutes. The air con is not switched on when it does this.
Secondly the car cuts out sometimes. After driving fine, I'll pull up at lights, the engine will start to fluctuate in revs then it'll slowly peter out. If I change to neutral quickly enough it can be stopped. Doesn't happen all the time but at least once after a decent drive. Also happens sometimes if I change from drive to reverse - the engine just drops away & stops. It starts again no problem. Any ideas on either problem?

Speedtoys

Of the updating work that you have done, have sensors, seals, AFM TPS, vacuum hoses..been part of it?

IE: A full & complete intake refresh?

OTR18WHEELER

just an idea and my first thought, the idle drop and stalling as you described could be the idle stabilizer valve, the buzzing could be a ruptured vacuum pot for the vents causing a vacuum leak which could add to the idle issue.

markpaul

I haven't done anything to it yet as only bought 22nd Dec (can't book it in until 5th Jan). That gives me another week to drive it and find out everything that needs looking into. Thanks for the suggestions - will definately look at full intake system and idle stabilizer valve.

Bertrand Daoust

The buzzing you hear might also be the little blower behind the interior temperature sensor.

Might need a little bit of oil. Not easy to get to though.

Speedtoys

Not much to 'look into' before doing a full top end, front end, and HVAC R&R.

Then you can look forward to the dirty work.

But those, need 100% accounted for before it'll ever run 'right'.

No shortcuts.

markpaul

Thanks everyone for your suggestions. Will let you know how I get on!