Woo, 3rd time posting in this thread.
Back in December, threw a single cylinder 3 misfire code. Cleared the code, never came back.
Last week, threw a cyl #3 misfire code again. I moved the coil pack to cylinder #1. The code followed...but it still threw a #3 misfire code as well!
I thought what the heck, replace the coil pack anyway and see what happens. While I was at it, I replaced the spark plug on #3. So now new coilpack and new plug on #3...and what happens? Misfires codes on #1, #3, *and* #4. WTF?
I'm going to try cleaning the MAF next. After that, injectors. After that, time for leakdown and compression test.
Keep in mind, it's now been a little over 2 years since my last adventure when I had my burnt valve on #4 and had the whole top end rebuilt.
Symptoms: It's idling like crap (was stalling at nearly every stoplight). On the first half of the idle relearn procedure after clearing a code, it actually idles a bit better, but on the second half of the idle relearn it throws a code and starts idling poorly again. Also a lack of power on the highway and fuel consumption has gone to crap.
Also found a crack in the plastic PCV crossover pipe that runs just in front of the intercooler. Doesn't really matter, since I had it capped off anyway when I installed the Grimmspeed AOS. I ended up breaking the pipe off at the crack and just putting the rubber cap over the new broken end instead of a little further downstream where it used to be. But that vacuum leak may have been at least partially responsible for some of the bad idle problems, at least.