Hello all, have a real head scratcher.
Working on a 2010 Tiguan that belongs to a friend, I have logged lots of hours working on this car as it ate it's timing chain and I did the R&R of the head with new valves, new timing set, etc... so the friend got a CEL, and it was the usual suspects: P0300, P0301, P0302, P0303, P0304, and P2187. I had him order a PCV valve and he brought the car and the part over, and I swapped it out. He got one of the aftermarket ones from Amazon for like 60.00. Well, on first startup, it was bucking and idle was all over the place and it would barely run. Tried to take it for a drive but it would stall at every stop. Pulled the hose from PCV to the intake manifold and installed a temporary plug in the intake manifold, cleared the codes, started it up and it was fine. Drove it for about a half hour, shut it off and back on several times, and it was fine and no CEL. Well, bad "new" PCV I thought. Had him order a genuine VW latest revision PCV. part arrives, I swap it out. Started it up. Misfiring and idling wierd, but not as bad as last time. CEL blinking but not on steady. It didn't stall. I drove it around the neighborhood, it was mostly fine. Took it for a longer drive, it was fine the whole drive, no issues. Gave it a couple full throttle rips up some onramps, drove it back home, shut it off, turned it on a few times, no CEL no issues.
I am going to do another cold start test tomorrow to see if the issue is still there before I return the car to him, but is it possible that the aftermarket PCV really was bad? And why would it still misfire on cold start with the new PCV? I am crossing my fingers that it behaves tomorrow otherwise I don't know what I will do.
BTW, when I did the head and chains, it also got new coils and plugs so all that should be good.