So I had my mechanic thoroughly clean the throttle body of the S70, both inside and out, to see what would happen - this took place the other night. I managed to drive it home and it was running just fine. In fact, it was running better after the TB was cleaned, as it started up better, and the car showed no symptoms of stalling when coming to a stop - even when it was warm, during normal braking at stop signs/lights, it would go to a really low idle and feel as if it wanted to cut out. Didn't happen after the TB cleaning - on braking it idled normally.

Just this morning, as I was driving to work, I noticed some strange symptoms - and I need your help. When I started the car, I saw that the rpm's went really high, to about 1800 rpm, before settling down to about 1200. I thought nothing of it and drove off. However, when stopped at a stoplight 10 minutes later, I noticed some strange vibrations coming from the engine. The idle became really lumpy and it started that thumping again - the one I mentioned that happened at highway speeds. When I parked it in the parking lot at work, I also saw that even though the car was thoroughly warmed up, and operating at normal temperature, it was idling fast, at around 1150-1200 rpm. Could that be a sign of the car running rich?

If I had to take a guess, it probably is a sign of the car running rich, and the thumping could possibly be a symptom of something worse. I'm going to have the codes scanned again, since the Check Engine light is on too.