Ok, we have a 2005 Mini Cooper Convertible. Service engine light came, but the car was running fine.Took it to Autozone to get the code. Codes were P0300 and P0304. The guy said to replace the ignition coil. We waited a week to save the money. Before we changed the coil, the car all of a sudden started to run rough. Felt like it lost a lot of power and idled rough. Within a couple of minutes, it goes away and run fine. This hesitation comes and goes. We changed the coil, spark plug wires and spark plugs. Still keeps dpoing it. What else???? Please help!!!!

 

P0300: general code for misfire
P0304: specific code for cylinder #4 misfire

Misfiring can be caused by a number of things. Here's your guide...

http://www.obd-codes.com/p0304

Since you've replaced the coil, plugs and wires, next up would be checking the fuel injector and compression for cylinder #4.