P0300 / Engine RPM speed @ idle

Cmike2780

I got a P0300 code (MIL) yesterday (Random/Multiple Cylinder Misfire Detected). I won't have a chance to have it looked at by the dealership until this weekend. The car is mostly stock except for K&N filters and a CBE. I don't know if it's bad gas or what, but I've never had this happen before. I did go to a different gas station the last time I filled up. It could also be the battery, but the car starts without a problem.

Already checked the following:
-air filters
-intake
-oil level
-exhaust leaks
-fuel cap

A few things some of you might be able to help me with:
I've noticed that the idle is sitting arount 1,000-1,200 rpm's when the engine is already warmed up. I can't for the life of me remember what it supposed to be. This is for the manual, in neutral. What's the normal rpm at idle for your car. I thought it was supposed to be around 700-800 rpm (warm).

I'm currently trying to run through this tank of gas and filling up with the place I normally go to (Sonoco). Should I try some fuel injector cleaner?

Should I clear the code and see if it comes back? Only problem would be the dealer giving me a hard time if they don't see it.

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[09][MB][6-Spd MT][Touring][Stillen Gen III][K&N][Borla CBE][Evo-R]