I have recently purchased an 04 mini cooper S from an individual. When I bought it from him he said that the plugs and the brakes needed to be changed. I changed them both but im still having problems.

I have changed the plugs to NGK Iridium
Ive also changed the coil and the plug wires. The car still misfires at Idle. It drives fine and I can drive it around but when i let it idle it will misfire. When I look up the code it is now a multiple misfire, but is sometimes only a misfire on cylinder 2 or 4. I can tell when it will misfire cause it will get to sounding almost like it has a cam. It kinda lopes at idle instead of idling smoothly.

I was just wondering if anyone else has had this issue or may know whats making it happen.

The car has some after market parts. It has an alta cold air intake, a bigger inter-cooler, and a 15% reduction pulley on the super charger. Im not sure if they put a tune on it after adding these parts and Im thinking it might have something to do with it if they did not.