So I am a new driver and I stupidly bought an A6 3.0l Quattro from a dealer without test driving or checking out the car in detail. I needed a car ASAP for work in Philly. I also did not realize that an Audi is a luxury car. So I get the car and start it and the "Ok Service" light comes on. The guy says we just did service on it and did not get a chance to reset the light.

So the first time I fill up the car with gas, I accidentally fill it up with Regular, not knowing I had to put 93 Octane. I drove maybe a couple hundred feet and the check engine sign came up.

Now the other problem I have with the car is that it accelerates really slowly, I'll have trucks at a traffic light accelerate faster than I do.

My last problem is, the engine seems to make a rattling/loud humming noise and one loud two second noise that seems like a blast or something when it starts.

I have been busy with work so I have not been able to get the codes for the engine sign, but I will have them next weekend.

The car is 109k on it.

Thanks!!