So the good news? (knock on wood). Although it shouldn't have anything to do w/my tach, replacing my PCV valve seems to have helped smooth out the rough idle on my engine at normal operating temps.

The bad news? On the test drive to see if the PCV valve did anything, My tachometer wasn't working at all when I started up the car and the needle stayed at 0 RPM's. However, shortly into the drive, the tach magically started working again

I'm guessing this is either some kind of sensor or wiring issue? Just need to know what to take a look at so I can investigate it further if it happens again, thanks!