Bad idle almost stalling. Solved
I've looked for two years to fix it and I just did and thought I would post it. While working on my AC I figured this out. I usually have the floor and defrost selected in the winter and AC selected in summer. Turns out that the defrost, even with heat, used the AC pump. I had too much pressure in the AC system from charging it 2 years before. When there is too much pressure the AC pump cannot turn forcing your belt to almost stop when the AC clutch kicked in. To see if this is the problem you are having try letting your car idle without A/C on and not on defrost, aim the air towards you. After a minute or two either use A/C or defrost, if it starts to studder remove some R134A from the high side, this is what I did and it completey fixed it.
If someone has already posted this feel free to delete this I haven't seen this posted anywhere on any site ever so I thought this would be a good place for it.