Recently my AC compressor took a dive. Clutch drive plate separated from itself and then jammed the clutch pulley and that was the end of that. While inspecting the damaged clutch I removed the belt and tried to spin the belt pulley. Choppy and stiff. I went ahead and had the whole AC compressor replaced. Picked the truck up and was rewarded with a smoother idle then I have in my newer VW. I'm thinking the faulty belt pulley on the compressor was causing a slight drag on the system? I use to have a very slight stumble while idling but it didn't cause drive issues and would not show up in the rpm gauge. After reading multiple threads it seemed this was normal with these engines. Just wanted to pass info along and say to check your belt pulley the next time you change you ac belt. Truck has all new spark plugs, wires, clean throttle body, clean MAF, manually cleaned fuel injectors and BB tune and it still didn't idle like it does now.