Idle surging and car shutting off

[myeshia91]

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?

[The Chauffeur]

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!

[myeshia91]

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!

Just did the stomp test. Got codes: 1215 Air Mass Sensor
1216 Throttle Potentiometer

Is the Throttle pontentiometer also a name for the TPS or is it something else?

[Ardvaark]

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.

[moroza]

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).

[The Chauffeur]

Stay away from generic O2 sensors.

"or at least a cheapie generic one, just to rule it out" :|

[myeshia91]

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.

Yea, I did get it from ebay. :/ It looks just like the one I have, but it has a thin wire (think of the wire in a lightning) coming from one end of the hot film to the other. My old part doesn't have that wire. Is it supposed to have that wire?

[myeshia91]

Here are pics of the two. The first is the new one and the second is my old one.