hello everyone. bought a used 07 rtl with 75k. 2nd day check engine light flashes with vtm-4. i bring it back and they change a coil pack and spark plug from number 4 cylinder. get 3 days out of it. same thing happens again and this time they change an injector. number 4 cylinder. get 2 weeks out of it and it happens again. just dropped car back off. what is going on? I'm worried they will not figure it out and I'm going to be stuck with a big repair bill as the lemon law coverage is almost up. any help would be greatly appreciated.