I feel really bad. I think that I gave my mom a lot of **** for messing up the car for nothing. I specifically told her not to fill the car up (because I knew she would put 87 Octane). Anyhow she went against my judgement and filled the car with half a tank of regular gas. Anyways without me knowing, I drove the car on the highway and suddenly it began to mis-fire and was very rough. So I brought the car to the dealer and they said there was a problem in the fuel system and a lot of carbon build up. That got me thinking. Is it possible that this would have happened 20 minutes after she filled up? Could is be a crazy coincidence that this happened right after she changed the type of gas?

There's no way that 87 octane could produce so much carbon that quickly or else they wouldn't use it in other cars...right?

any ideas?