Before i would spend any more dough. do a cylinder leak down. you want to make sure you have less then say 10 % leakage. also at the same time if you have more then 10 % you can figure out what is going on by listening for where it is going. also what about a bad injector ? i agree you may have more then one problem. just do not make the mistake and spend a bunch of money on needless parts if the valves or rings are junk.v i would think you could have it diagnosed for about 100 bucks at the dealer. it may save you money in the long run by not buying needless parts.