Have done a lot of work on mine lately , any new questions we can find answers for ?

hi! I got my vette about 4 years ago..it has the original engine with all the original parts on and since the day i got it i had never had any king of problem until last week when, after i was driving the car for about 50 miles, and it was running just fine, i got a check engine light and it running rough!!! i started burning to much fuel and i barely got home.I tried to turn off the engine and back on and i realized that if it's at idle power it runs well ,even if the check engine light is still on, when i give gas it starts running rough and loading up with fuel!!! What it colud be???????
Thanks in advance....