Ok Sometimes when I start it, its fine. and sometimes it turns and then give up and turns again and a big backfire(noise) is coming from the motor and it starts.

What is the problem?

 

bump

 

check the coil for the spark plugs.... that's what happened to me. I had to take it to a dealer to find out though. But it could've been alot worse then it was. So make sure your coils touchin your plugs. And/or your injector it might not getting the fuel. I also had my injector cleaned.

Tae

 

A back fire or pop from the intake indicates your timing is off.
Check your crankshaft position sensors (POS & REF)