Possible weird sound from motor
The car is a 2005 GT that has gone 110 000 km.
To keep it short: A couple of days ago, on the highway, I needed to shift gear to idle. Doing this, the RPM dropped to idle (approx 1000?), while still moving at considerable speed (110-120 km/h). I then shifted again to the fifth gear, as careful and gentle on the clutch as I could. However, it still was kind of a fast reving up to 3-4000 rpm. At the same time I got the dreaded "Motor control system failure" error. I immediately shifted to idle again and stopped at the side of the highway.
I shutdown the car, swore a little (that means a lot), then tried starting it again. No error message, nothing sounded or felt wrong from inside the car. I started driving, nothing has changed compared to earlier with regards to the car handling or acceleration. I stopped at the next suitable place. Listened, reved, opened the hood, but couldn't notice anything strange. I googled for a couple of hours, but came up short of an explanation.
Today, a couple of days later, I went outside the car with it in idle. When I heard the motor sound from outside, I got the feeling that something, altough I can't pinpoint what, sounds different than before. A "rattling" sound wouldn't be entirely true, but it's the best I can come up with. It's hard to say since I haven't had the car for more than three months and I'm not particularly experienced with car motors and how they should sound. It sounds good while reving, it's mainly when the car is in idle that it sounds "weird". Also, when idling standing still with the door open, I've felt a faint smell of gasoline-ish (but not spot on) smell with a hint of something burnt-ish in it.
My question is, do you think something may have broke? What are the usual suspects when reving fast from 1000-4000 rpm? Or am I just imagining things?