I have a 94 525i with 267k miles. The check engine light has been on for a while. I was getting the code for the MAF. I replaced that today and the CEL went off immediately, however, it started having a surging idle when I let go of the gas pedal. When I come to a complete stop, the car starts to surge and even surge forward even if I have my foot on the brakes. Sometimes the car just shuts off when I come to a stop. And sometimes the CEL will come back on after the engine surging. I haven't done the stomp test again yet, but will do tomorrow.
Any suggestions on what could be the problem?
Unfortunately, those symptoms are relatively common to many issues... That said, it sounds very similar to my experience with a bad oxygen sensor: idle surges, intermittent CEL, stuttering, although mine wasn't shutting off; sometimes I was able to make the CEL go away by shifting to a higher gear (when possible), you could try that if yours is a manual, just to check.
If the stomp test shows no codes, I'd try and get a good used oxygen sensor, or at least a cheapie generic one, just to rule it out; if that doesn't work, throttle sensor and idle control valve would be my next suspects. As I mentioned, there's a couple other things that can show similar symptoms (even a bad ECU!).
Hope this helps, and good luck!
Where did you get your MAF? If you bought a cheapy on ebay verify that the construction in the airflow area is identical to the one you removed. The cheapy I bought on eBay was the hot wire type and not the hot film type that was required. I had all kinds of surging problems with the ebay cheapy. Luckily, Ross sold me a good used one here in the forums that was the proper hot film type and it solved the problem. Still working great today. The only other thing I can think of is a vacuum leak somewhere. A smoke test will help you find it.
Stay away from generic O2 sensors. Throttle Potentiometer should refer to the TPS, yes (it could also refer to a pedal sensor which your car 98% does not have).
Here are pics of the two. The first is the new one and the second is my old one.
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