As a follow-up to my original post, about oil drips....
I have been having some other on-and-off symptoms:
- occasional CEL's, with the codes being P030x (x is the cylinder number). This code indicates a misfire in cylinder x. They occur either on one whole bank (1, 3, and 5, or, 2, 4, and 6), or sometimes all six cylinders. Sometimes there is a barely-perceptible "stumble" of the engine when these happen, but often there is no indication of an actual misfire....
- just recently, when inching along in slow traffic, I'll let off the gas, and the idle will momentarily drop to 500 rpm, or even a tad lower. It almost always recovers, but on two occasions the engine has died (and then started right up). If I'm in Park, and blip the throttle, the rpm after the blip also dips too low, before recovering.
Mostly for the last problem, I decided to replace my PCV valve. It "rattled", but still seemed gummed up, and was never closing fully. My suspicion is that it wasn't opening fully, either. (Actually, in a PCV valve, the full-flow condition is basically the middle position of the moving part, with low-to-moderate vacuum. High vacuum, at idle, or foot off the pedal, pulls the moving part the farthest, but this is actually a low-to-medium flow position.)
The new PCV valve has solved the low-idle problem. The P030x DTC's were intermittent enough that it will take some time to tell if it also cures that problem. But, a gummed-up PCV valve CAN result in a too-lean condition under some circumstances, that MIGHT trigger those codes...
Finally, a PCV valve that doesn't open fully (or, more accurately, open to its "full-flow" condition) can result in excess pressure build-up in the crankcase, contributing to oil leaks and drips. So I am holding my breath to see if my slight oil leak stops.... (Unless some permanent harm has been done to the gasket or seal....)
I hadn't thought to check this before replacing the PCV valve, but one thing you can do to check for various kinds of PCV issues is to remove the oil dipstick, and see if you have pressure in the crankcase. If the pressure is bad enough, you can definitely feel it by putting your thumb over the dipstick tube. In really bad cases, the pressure might push the dipstick up out of the tube.... You might also have to rev the engine to see if you get positive pressure while revving. Those symtoms would all argue for replacing the PCV valve.