I took my truck in for extensive routine maintenan...

I took my truck in for extensive routine maintenance. Several fluid changes, an inspection and a valve adjustment. I picked it up a couple days later with a $1600 bill and a check engine light. I was told it was a preexisting condition. If that were the case why didn't they mention it the two times I had asked if they had found any problems? After all, I did ask for an inspection. I feel I was overcharged and they clearly didn't perform the service I asked for and now I have a problem to fix I didn't have before.