frob

Hi folks, new member here, desperately seeking help!
I have a 99 A4 1.8T Quattro (B5,~ 170k Km), which about a month ago started doing this while on a long car trip, seemed to happen only occasionally but now consistently whenever the car is started cold-
no problem starting ( instantaneous) but idle speed is unsteady, and when taking off, a few seconds later the engine really bogs down, hesitates, gives an occasional small backfire, and just seems to loose practically all its power, barely being able to accelerate at all. flooring the pedal only makes it worse. then, after a minute or 3 of this, the car surges forward and everything seems to go back to normal, for the remainder of the trip.
The CEL has been on since i got the car, i took it then to an independent Audi-VW mechanic and they said the turbo wasn't working ( no boost) due to a broken wastegate, they found bits of it in the front of the cat. Other than having a little less engine power, the car has been working fine and was drivable. I was waiting to find a good deal on a used turbo to change it, until this last problem appeared.

The mechanic spend an hour checking things last week and came up empty - he's baffled. Coils are good, changed plugs, no apparent vacuum leaks.
Said the O2 sensor looks to be dead, but it doesnt explain this problem on its own - might be a bad cat, plugged or craxked core moving around , but every experienced mechanic / muffler shop says when the cat is plugged, it stays plugged, so it wouldn't act intermittently-but-consistently like this is.

Scan codes read:
O2 sensor - B1S1
Charge pressure deviation ( i.e. turbo not working, knew about that)
B1S2 Limit reached
LTFT B1 Lean
LTFT B1 Rich

Any ideas ? Could this all be caused by a bad O2 sensor, or is that just a symptom of a dead cat?

frob

Well, i checked the Cat, and its in great shape, so thats not it. I ordered an 02 sensor and will change it tomorrow, and check fuel pressure.

Any ideas? anyone out there?

MACK5

HAVE U CHNG TB WHEN? AND THE MAF HAVE U CLEANED IT?

quattroRhat

yeah, I think I have the same problem with my 98 B5 QTM, I drives really poor, no power at all only torque it seems, has anyone find a solution, think its MAF, but not sure.

frob

Changing the TB & WP next week, or whenever the kit arrives. Fixin turbo too.
Cleaned the MAF, no joy,
changed the front O2 sensor, that did it, now she runs fine. CEL went out on its own too!