I searched for this and found tons of threads on rough idle but mine seems different than most. My truck idles at 500 rpm when in drive, very smoothly. When it's in park or neutral the idle kicks up to about 600 rpm and really starts shuttering and missing, dropping below 600, idling back up and so on. It only does this after it has warmed up and I have driven it for a while. When it is cold it actually idles fine, the idle is higher (which I have read is common), but it runs fine. It drives fine at highway speeds and seems to have plenty of power. Some history, my cruiser is a 96 with 172K, I just did TB cleaning, plugs, wires, PCV valve and grommet, replaced vacuum lines, replaced air intake hose (ripped old in half during tune-up). Mileage dropped off about 2mpg after the tune up, but I can't isolate that mileage drop to my tune-up because of winter blend fuel being used in CO. I am in the midst of running a tank with BG 44k right now, but I can't tell that it's helping at all and I have almost ran the whole tank. The truck will throw a P0401 code if I am on the highway for a long time after it has been going 65-70 + for a while, but it never throws it around town. Is there a specific problem that is associated with this? I know the wiring harness that melts is a common suspect-I plan to take a look this weekend. Could I have screwed something up on re-installation? During the tune-up I noticed a very small crack in the hose surrounding the base of the PCV valve but it is very small. I was thinking if I messed something up on re-install it would not run well at higher speeds and acceleration. I run 85 grade fuel would that make it idle poorly in park/neutral? Any usual suspects I am missing? Thanks.