The check engine light has been one in my car for a while, but l have taken it to a mechanic three times and had the exhaust valve replaced.

In the mornings, l have to give it some gas while starting so that it will not sputter and then just stop.

Any reasons that my check engine light is on?

WHAT DOES THAT AIR FILTER LOOK LIKE NEEDS TO BREATHE
SOME TIMES IF YOU DISCONNECT THE BATTERY THE COMPUTER WILL CLEAR AND SHOULD BE RESET WHEN YOU START ER UP

Disconnecting the battery does not clear the code it only turns off the CEC light and the light will come back on unless you have addressed the problem properly. The reason for the light could be anything from an O2 sensor, MAF sensor, a bad injector, etc. It is best to take it to a mechanic with an OBD2 scanner and have them pull the code from the computer and find out what is wrong with your car.

you can buy a basic obdI l scanner at autozone for about 80 bucks. it better than taking it to a mechanic and charging you 50 bucks just to pull the code.