Why does the service engine soon light goes on and off on a Chevy Camaro Z28?

everyone should have a manual for their vehicle, and a professional shop manual should be available at the library in the reference section for FREE...make copies of the right pages and fix your vehicle like a PRO! :) good luck Dave :) there are plenty of reasons. you just have to read the code, correct the problem, and then reset the OBD. If you have taken the cats off your exhaust system it tends to do that, or it could be the vacuum line to the distributor has a leak or has come loose.