Ok i was cleaning the K&N filter n i unplugged the sensor n when i was done i put everything the same way it was and i started the car all of a sudden i hear a nasty knocking in the engine.What could it be please dose anybody have any idea

 

Check ur oil.

 

Then clean maf, reset ecu, throttle body relearn, idle air volume relearn. All documented here. Let us know if you have questions.