For some reason if my car sits at idle for more than 10mins my cel will come on, but more than likely go off after awhile of driving. Any ideas on what could cause this! when i check the code it says random missfire. You can also hear knock come from the motor every now and then

 

Bad CP?

 

check your coil packs, they can operate differently when warm. This could also be an alternator/battery going out, if the power to the ignition is intermitent the coil may not get enough for a spark.

Bad coils shouldnt cause knock, per se. they will cause an imbalence which may sound a littel weird, but if you are getting true knock, check all of your injectors. The misfire may be fuel related, and the knock is due to the overly lean condition. Not sure how the time/condition factor works on this one though.