My check engine light is on and sometimes flashes
I believe it's a vacuum leak I replaced the PCV valve and cracked elbow going to it but
still have the problem. Seem to hear a hissing sound against the fire wall on the
passenger side. Also could it be a bad o2 sensor?
check for engine codes. also, with the engine cold and running, spray some carb cleaner around in there to see if the idle changes, it may help you narrow down your search.
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