What causes a 1997 Dodge Intrepid to idle rough after changing the plug and plug wires when the check engine light gives a code 5 cylinder misfire?

Answer 1

Hi

Well, you have your answer: you have a cylinder misfiring. You need to know which one it is and why.

Taking two pieces of stick, or a pair of WELL INSULATED rubber-handled pliers, start the engine and take off the first plug wire. If that cylinder is good, the idle will get much worse, and it will probably even stall, so you know that one is firing if the engine does not change. Keep going through the plug wires until you pull the wire and nothing changes. That's the bad cylinder.

Pull the plug and look at it, and compare it to the sample photos that usually appear in the workshop manual. If the electrode has burned away you have a different problem than if the plug is fouled with burned oil, or if it is soaking wet with gasoline that it should be burning but isn't.

If you recently changed all the plugs, did it run allright for a while, then go bad again, or did changing the plugs make no difference? Because that would indicate something more likely wrong with something else and not the plugs themselves.

Is your intrepid equipped with the 3.5 liter engine? If so you likely have an air intake plenum gasket leaking. The fact that the pcm has stored a misfire code for cyl # 5 should give you a starting point to check for this condition. With the engine running at normal idle speed in park briefly spray some aerosol carb cleaner at the area where the intake plenum (upper ) is bolted to the lower intake (at #5 cylinder intake runner). If the engine smooths out when sprayed or the idle rpm increases or decreases noticably then you need to remove the upper plenum & look for a section of the gasket cracked & sucked inward, or missing entirely. This is a common condition on the 3.5. if the plenum gasket seems to be intact & no change is noted with the carb spray then you may have an issue with the fuel injector on #5 cylinder. Good luck!