i had my friends dad run i check on the computer to see why the emissions light kept coming on. at first i thought it was a leaky gas cap, after i was reassured that wasnt it, it came up as 5 different things from a leaky gas cap to a tranny problem. i replaced the egr valve and a blown solenoid. 2 days later now , the emissions light is back on and ive had the computer debugged of all the codes atleast 4 times. what is wrong?