07 trailblazer, 4.2l engine, 125k miles. Initially threw a p0306 code, easy fix i thought. got home, tested coil and sure enough it was bad. replaced it. next day starts throwing a p0300 code with an audible ticking sound; **** me right. so i just decided to do a tune up, replaced all coils and spark plugs. replaced fuel filter and did an oil change. start the vehicle up and still a p0300 code. check plugs and coils again, all good. it does bog down after a minute and there is smoke coming from exhaust. pulled throttle body and cleaned it. still same when i start it up. could it be the vvt or water pump? it doesnt over heat and oil pressure is above 30. i am dreading the possibility its the valves or other engine problem. any help would be welcomed.