S50 Intermittent Surging and CEL problem

[M3PO]

Hey guys, my S50 swapped car has a weird issue. Occasionally when I am accelerating normally in 1st, 2nd, and 3rd my CEL will come on for a second at about 3K RPMS, then go off. It does it in each of the three gears but not 4th and 5th. It doesn't happen often and the car acts normal so I don't know how to diagnose it.

The other problem is that occasionally if I'm cruising along in in traffic at moderate speeds and constant throttle (2500-3000 RPMs), the car will lurch or surge. Again, it's very intermittent.

The car runs great otherwise. Except sometimes it feels like it's a little bit down on power (old knock sensors?). I also have a slight miss at idle.

Ideas? Thanks guys!

[sweet3]

could it be your vanos?
Have you tried "stomp test"? It might throw a code

[M3PO]

could it be your vanos?
Have you tried "stomp test"? It might throw a code

My VANOS is noisy, I know that for sure. I tried the stomp test when I finished the swap but I was under the impression that it wouldn't display a code unless the CEL was already lit.

[mpowerful]

It stores codes.

[M3PO]

Stomp test revealed P1226, which the internet says is for the knock sensor. I will report back after I swap them out.

[amcink]

Becareful with 1281 then you need a new DME

[M3PO]

Becareful with 1281 then you need a new DME

Not sure what you mean. It never threw 1281.

As an update, the rear knock sensor was busted all to hell. CEL has not reappeared. I haven't experienced the surging again either.