Today I got another clue about the transmission problems. If you remember, the car had trouble shifting during the last few trips to the track. I tried messing with tuning, reinstalling the idle control valve, etc but nothing has worked. Meanwhile, I've also been getting intermittent "cog of death" warning light, on the dash. Usually, it comes and goes too quickly for me to hook up a diagnostic tool.
But today, I was flashing an updated tune, and the "cog of death" popped up when I turned the key. So I immediately fired up INPA and scanned for faults. Here's what I got.
And this started an internet search rabbit hole...
Apparently, "getriebeschalter" means "gear switch" in English. But I don't see a P-code for the error. I'm assuming the "60" is the error code. So I searched for that. And apparently, this trouble code points to the gear selector switch / sensor. The symptoms of a faulty gear selector sensor seem to be similar to the ones I'm experiencing.
Unfortunately, RealOEM.com has no info on this. The web page literally says "no parts found". Wonderful.
But luckily, another E46 Fanatics member did a writeup on this. Here's the link:
DIY: 5HP19 Transmission: Selector Switch
When I get a chance, I'll pull that switch and see if I can fix it. I'm also thinking of making a video about it, in case someone else has the same problem.