What's up guys, after posting this in the regular S60 area I decided to also post in here, despite not being an R, because A) these cars are like 95% the same and B) I figured I would get a response faster since I'm taking it in otherwise in a day or two!
06 S60 T5M, 210k, Stage 1 Hilton (soon to be stage 2+ when I get that virus check... )
So for a while it's been missing or something RIGHT AT max boost, but no codes; it doesn't feel as bad as a miss, more like... a weak miss? I thought it might be a weak spark, but new plugs didn't help and removing the air filter helped a lot, so I switched to thinking it was the MAF with a cracked housing (pre-sensor) causing intake air turbulence at the sensor and a bad reading. Anyway, the other day the CEL came on for the MAF so I swapped it out and it started running even worse!
The newly revealed problem is that it kinda misses occasionally when idling and near idle throttle, but drives fine normally (except the boost thing is still there). Basically some symptoms typical of fuel trim issues? Also the CEL is on, it says for the MAF again which is obviously not accurate... The interesting thing is that as of a day or two ago it has stopped doing the 2k rpm rev to warm things up like it's supposed to, which perhaps indicates something wrong with an O2 sensor or something telling the computer that the emissions are already fine.
That state return just hit, so I'm planning to take it in in the next day or two if I can't find anything on it myself, since they have the diagnostic tools. Just wondering if anyone else has had this problem, and they knew what to do. It seems like this new symptom would be characteristic of a particular sensor going bad, or some other specific issue, and it can't just be me.