check engine light

What is your question?

I just recently had my timing belt changed on my 95 lhs, and before I took the car it had a little idle shake, then when I picked it up, the idle was a little worse but the car ran alot better, then while waiting in the drive thru of mcdonalds the engine light came on, in which it never did before, only after I come from a auto shop. The mechanics always say the engine is good, so what could be the problem