Hey everyone I'm new here!

I've been looking for an answer here before. The story goes like this:

I took my car to a shop where they did a full timing job, all the tensioners, the chains, but not the vvti actuators ( i think thats what they are called, im not a native english speaker ). So when I got the car back, it has got a check engine light, and when i delete it, it goes away for like an hour and comes back. Now, I know most of you will tell me to bring it back, but I really don't want to since the timing took them over a month, and I would guess they would take another month to resolve this minimum. The engine has some kind of backfire 1 out of 5 times when i start it. Runs well, gas mileage got a bit worse since the light is on but not that noticeable. What should I look into? I'm fine with cars, the only thing I don't want to do is to mess the timing up. Help please!