Just picked up an old wagon wasn't running the best now seems to be worse. changed plugs, wires, cap & rotor, new air filter, changed the oil, and cleaned the maf. (with MAF cleaner) It idles and revs just fine, though under load it stumbles and sputters. The check engine light comes on after a while but I don't know where to plug in and see what it's saying. Any help would be fantastic.