I've got an issue with intermitten rough idle in my 85 K10's 305. Steps I've taken: -Rebuilt the q-jet (including new accel pump). The APT is set at 2.5 turns out as are the mix screws. The mix screws were set with a vacuum gauge. -Set initial timing to 4° BTDC (if the marks are accurate) -Disabled the ESC -Checked the vacuum advance can (which is hooked up to ported) -Checked the mechanical advance weights (they move smoothly and snap back) -New cap/rotor/wires/plugs -Checked the EGR (moves and returns freely, diaphragm seems good) -All new vacuum lines The idle quality seems to fluctuate randomly. If it's acting up, it will idle rough at every light or stop during that trip. On the return trip, it may idle ok at every stop. When it's acting up, it seems to load up, idling worse and worse the longer it idles until the whole truck is shaking noticeably. I always thought loading up indicated it's idling rich, but I get no black smoke or rich smelling exhaust. It passed emissions last weekend with flying colors when it was idling pretty rough. It never dies or seems to fluctuate wildly in rpms. Also when it's acting up, there will be a bog or flat spot when accelerating just off idle. This hesitation is sometimes present to a lesser degree when it's idling ok. Sometimes it'll ping for a fraction of a second when tipping in from idle. It never pings any other time - just when leaving from a stop. I have searched and searched for a vacuum leak. I replaced all vacuum lines. I've tried spraying carb cleaner in the area several times, and I haven't pinpointed anything. The carb itself hisses a whole lot. I suspected the throttle shafts. The throttle has a little bit of play in it, but spraying the driver's side linkage with carb cleaner doesn't seem to affect the idle. At one time the throttle was hanging up, and depending on how I released the accelerator the idle would vary by several hundred rpm. I put on a new throttle return spring and that seemed to cure it for the most part. If I gingerly release the accelerator it'll probably stay idling 50-100 rpms higher than if I let it snap back from WOT. If the throttle shaft was worn badly enough to cause this poor idle, I would think spraying carb cleaner on the driver's side linkage would affect the idle. I'm beginning to wonder if I have an internal leak (bad intake gasket)? Or the carb has an interal vacuum leak. I know that the air horn on my carb is pretty warped, but again spraying carb cleaner doesn't seem to affect it. #8 spark plug was kinda greasy. Could a burned valve only cause idle/low rpm issues, or does that usually cause a miss at all rpms? Any ideas?