Toyota Repair: 2001 echo, gas cap, three times

Question
when starting my echo it starts rough or slower than before
it runs fine after, ps a check engine light is on its been checked three times at dealer , had gas cap replaced could it be plugs or a sensor. thank

Answer
What were the diagnostic trouble codes that made the check engine light come on? If it was at the dealer three times then you should have that information on the repair order receipt.I also need to know exactly what the dealer did or recommended, if anything, to fix the problem.