rough idle, SOMEONE PLEASE HELP!
For Several months now, I have been experiencing a minor problem with my engine that is driving me up a wall. When I start my engine, it runs perfectly. However after the engine warms up it idles rough and actually runs a little rough throughout the entire driving range except at highway speeds. The roughness is characterized by a minor, but notable pop or put in an otherwise smooth running sound. It's not rhythmic but intermittent and it only occurs after the engine is warmed up. If I allow the engine to cool and start it up again, it's gone until the engine warms up. Right now I have several modifications to the engine. I have a performance ignition system with 10mm cables. Cold Air Intake. Street style exhaust header. 3 inch cat back system and 3 inch underdrive crank pully. At this point, I have had no check engine lights activate and the condition is not worstening. I have however heard what I think is a notable hissing sound from the rear of the engine compartment. It is noticeable over the normal engine noise and I'm not the only one who's heard it. Currently, I've replaced the O2 sensors, the pcv valve. I've pressure tested the pcv hoses and made sure there is a good seal on the nozzle where pcv hose connects to the manifold. I've also replaced the fuel filter. At this point I'm thinking my only option is to remove the intake manifold and check for cracks as well as replace the gasket as I'm convinced the piece of crap, PLASTIC intake manifold has cracked somewhere. I was wondering if anybody has experienced similar problems and what the hell was wrong. I need to know if I'm heading in the right direction with the leaking intake manifold theory.