Pontiac Repair: 1999 SUNFIRE 2.4L, jump time, miss fire

Question
I HAVE A ROUGH IDLE GETTING CODES P0300 MULTI MISS FIRE
I HAVE CHANGED COILS,BOOTS,MOD,TEMP,TPS,AIR FLOW,DID A INJECTION PERG CHANGED COMPUTER STILL RUNS ROUGH AT IDLE IT RUNS GOOD GOING DOWN THE ROAD IM A AUTOMOTIVE TECH,I GAVE UP AND LET MY FRIEND TAKE IT TO SEE IF HE COULD FIX IT HE WORK AT A G.M. DEALER HE DO'S NOT KNOW WHATS WRONG

Answer
Hey Dan:

I would look at compression on this engine both static and running. Take a look at what the MAP reading is at idle. It me be a bit deceptive due to an erratic idle but if it's high this could have jumped time on one of the cam shafts. Is there and engine noise from the front timing cover? I have seen these engine jump time on the exhaust cam and cause all kinds of wierd stuff. Has the water pump been changed recently? if so the whole timing may be off on it not just one cam. It's a place to start. Good luck :}