What car are you talking about?
Have you checked for any codes? Not all codes will set an engine light so get them read even if its not on.
You should put your car info in your sig so you don't have to keep repeating it.
First guess would be tuneup and make sure the plug wires aren't near the o2 wires by the firewall
Second guess would be battery & ground connections.
Third guess would be the dreaded intake leak.
Forth would be MAF sensor or connections.
Again these are just guesses. Better advice will come with more info.
98 SSEi 111,222 miles.
Intense PCM, LS6 Valve springs, PEMS, FWI. Hawk Street Pads.