My wife complained about the heat not working on her car so i checked the coolant level and found the coolant overflow tube had been cut by the belt and the car was low on coolant. So i added it and noticed that the cap was nasty with the dexcool sludge. So i added coolant and bled the system and the heat was still not working. I then backflushed the heater core and refilled. Temp still bouncing around and heat not working. So i decided to flush the whole system as that sludge was thick and nasty. Same thing no heat and now the car develops a bad miss( almost like a heart-beat). So i take the car to a shop and they say it is a blown headgasket( they did the exhaust in coolant tester and it came back positive). So i changed out the headgasket and now my car has heat but it still has that terrible miss(gets a little better when i pull the MAF senser). i put new plugs in it when i did the swap and i tried the coil pack off my 99 GTP to see if maybe it was damaged by water getting on it but it did not fix the problem. The car in question is a 2005 grand prix Comp G and i have a 99 grand prix that works that i can borrow parts off of to see if it fixes the problem so i dont need to throw money at parts. I am at a loss with this car. Anybody got any ideas

Thanks

Scott