My 1999 dodge neon highline has 935000 miles. The check engine light came on about 5000 miles ago (i'm disabled w/ a smaller than usual income and health costs didnt allow immediate repair) here is the symptoms i've encountered; I recently changed the spark plugs and all 4 were oil covered(worn valve guide or piston rings?)The car ran great for two weeks and now the running symptoms have returned but not as bad. The running symptoms: engine stumbles on acceleration, with an occasional backfire. In addition to that, when I turned on the air conditioning the problem magnified by 3 or 4 times(fouled plugs, probs w/ fuel injection, clogged fuel filter, engine control system probs, intake manifold air leak, egr system malfunction, intake gasket sealing alignment.)Diagnostic test indicated misfire on cyl.#2. My question is this : are these symtoms and indicators caused by one problem or two, there are so many cross over symptoms that it has thrown me.
Have someone take out one of your new spark plugs and check it for oil. If it is oil covered or " fouled" you may have bad piston rings. If no oil on plugs spend about $15 on two bottles ofChevron's Fuel System Cleaner with " Techron". It really does the trick to clean up nasty fuel rails and injectors. Also have the air filter & PCV valve replaced and check the vacuum hoses and fitings. If you have a vaccuum leak, you will be able to hear the suction under the hood or find it by spraying carburetor cleaner on the hoses and fittings. The air conditioning tips me that it may be vacuum related.