I am working on a '89 535ia.
Sometimes while driving the check engine light will come on, and come off if you release the accelerator.

The code says: O2 sensor.
But when I check the vacuum, I have a very low reading (10in) and if I accelerate, the car wants to stall then the RPM picks up and the vacuum reading reads 0....

Spraying carburator cleaner all over the engine didn't do a thing...

The car just warm up when the engine light comes on...
The car runs pretty rough when you just start it.

ARG.