O2 sensor problem
 

'99 323is, manual, I had a problem with balking acceleration,cutting out and missing between 1000rpm and 2000rpm, checked and got a "Pre Cat O2 sensor code". I changed the O2 sensor closest to the cat, still same problem, same code, changed the other O2 sensor, same problem, same code. All I can find are just these two O2 sensors, is there a third O2 sensor further up on the header down pipe? At 70 mph on the high way I get 30+mpg just like I have for the last 120K, acceleration in 1st and 2nd can be balky unless I feather the gas pedal . I really dont want to go to BMW for repair, any ideas will be appreciated.

I am not certain about the 323, but it should have either three or four sensors. Either two fronts and one rear, or two fronts and two rears like a 328. If your exhaust manifold is split into two banks of three, it has two sensors.

What was the exact code?

You should have two precat sensors. They in the engine bay on the manifold.

I have found and changed two pre cat sensors, both are before the cat and after the exhaust down pipe. Since I have changed both sensors what could be causing the pre cat sensor code?

It depends on the code.

It could be a damaged wire.

The car is in the shop right now, it is stuck in first gear, dont ask me I dont have a clue as to how or why, anyway, when I get it back I will confirm the code and check the exhaust manifold for more sensors. I dont remember the code number , but in he Peak book it was "Pre cat O2 sensor".