John, take a deep breath and start at the beginning. How does the car run?
Do you take it on only short trips?
I'd start with a new air filter and pcv valve, these are cheap enough. Next
I'd run a bottle or two of injector cleaner and change the oil and filter.
Make sure the wires and plugs are in good shape, although I suspect you'd
feel the misfire if this was occuring.
To equate only this to a bad head gasket or broken ring I think you'd have
other symptoms (major symptoms)
I've answered inline...
> John, take a deep breath and start at the beginning. How does the car run?
Runs fine; great idle; no problems that I know of
> Do you take it on only short trips?
Most trips are about 30 minutes each way (that's my commute to work), rarely longer than that. But it's 70+ mph most of the way
so I think it gets good and warm.
> I'd start with a new air filter and pcv valve, these are cheap enough.
I have a K&N that is clean. I have bought a new PCV valve but when I realized the upper intake has to come off to change it, I
decided to do it "another day."
> Next I'd run a bottle or two of injector cleaner and change the oil and filter.
Oil & filter were just changed (about 400 miles). I've never tried injector cleaner; any recommendations?
> Make sure the wires and plugs are in good shape, although I suspect you'd feel the misfire if this was occuring.
Not sure what a misfire feels like; one time it ran really crappy for a few miles, extremely poor acceleration and sort of
jittery, but then it just snapped out of it and started running normal again. Only did it that one time. Would that have been
misfire?
> To equate only this to a bad head gasket or broken ring I think you'd have other symptoms (major symptoms)
I recently replaced the O2 sensors and the idle air control (did them on the same day), and I can't say for sure whether the
problem pre-dates that or not. I changed the IAC because the old one was always a little sticky, even right after cleaning;
replacement was just $50 so I said what the heck. I changed the O2 sensors simply because the old ones had 295k on them and I've
read that the replacement interval on them should be 70k.