[47Straight]

So, the last couple of days I've had issues with the idle on my 2013 335i. It started out with the idle being a little rough and it developed into an unstable idle where at stops it would almost constantly rev between 600 & 750 RPM, occasionally jumping up above 1000. Then it developing into this uneven idle followed by dying. It'll restart fine, but after a few seconds of consistent idle it goes right back into this little routine. Now, it the throttle will even jump a bit, and feel like it's down shifting during mild acceleration at slow speeds. Once I get up to 40+ MPH it seems fine.

It started out just an occasional occurrence, but has become a consistent problem over the last few days.

So, I ran codes and it gives me a 128E01 fault code. I can clear it, drive a bit until the car acts up, and the code is back. The fault explanation is: Lambda probe upstream of the catalyst, electrical: interruption Nernstleitung.

Obviously, the code sounds like the pre cat O2 Sensor is bad, but I just wanted to confirm that the this is the kind of symptoms you'd might expect to see from a bad O2 sensor. I did a search and found things like poor gas mileage and rough idle, but nothing to this extreme.

Also, does anyone have any experience with a bosch O2 sensor vs. the OEM?

Any feedback before I order the sensor tomorrow would be greatly appreciated.

[47Straight]

Originally Posted by 3A53

In my experience the pre cat O2 sensor on a turbocharged engine is always the first to go.

On my N20 the idle kept getting worse over about a week until it would die at most stop lights. It finally threw a CEL and P code. Replaced the upstream O2 sensor and all is good.

On my car both original sensors were made by bosch. The upstream was on genuine BMW closeout and I elected to do the downstream at the same time with a bosch universal. No issues with either and my furl economy has gone up about 1.5 mpg.

Thanks for the input. That sounds almost exactly like what I've been experiencing. On the bright side, with the N55 I can get to the pre cat sensor from above without dropping the cat. That being said, I'm tempted to go ahead and do both. I can get both bosch sensors for about the same price as one OEM, but I have to drop the cat to get to the post cat sensor.

[Bmw doubles]

What was the outcome on this? Did the precat sensor replacement resolve the problem? I ask because I'm getting that error too on my N55.