bksnogaro

Wanted to get opinions to see if I am heading in the wrong direction.
2001 B5 S4. tiptronic
Dealer replaced front brakes an heat shield after the car was shaking on idle and acceleration as well as sulfur (rotten eggs) smell and smoke coming out of front pass. side wheel well.
Brakes are good now, smoke/burning gone. But car still shakes like crazy when driven with blinking engine light. Serious loss of power and horrible gas mileage in the last few days. Occasional smell of sulfur.
CAT replaced last year under 80k warranty.
Dealer now says 02 sensor bad and needs to be replaced.
Hopefully this fixes it. Will be $3000 after the 02 sensor replaced and all above repairs including 80k service.
If not better after 02 sensor, what else could this be?
How far do I go for a car that's only worth about $9K?
Thanks

donromani

Is it front or rear O2, and which side? I've had the rear O2 fail on me but all you get is a check engine light that stays on and somewhat worse gas mileage. That sulfur smell and engine stutter sounds more serious than a mere faulty O2 sensor.

complacentsee

Agreed. That sounds like boost leak, a faulty spark plug, or coil pack. O2 sensors don't cause flashing CEL IIRC.

If your wondering how much to keep sending on the car. Maybe now is the time to get out???? I would make you an ultra low ball offer, but I don't want to inadvertently insult you.

RolledMySTi

I could be the O2 sensor, but I doubt for that serious of a misfire. Most likely a boost leak. Time to learn how to work on the car yourself or sell, because it will get expensive pay the dealer to track down the misfire.

fallout

Boost leak. Most likely torn throttle body boot (very common prob and had same issue on my 02 s4). TBB is a 30min DIY repair.

Fix the leak FIRST and then see if there are still O2 sensor issues.