2000 4.2s AC went out and had to get it fixed. AC place pulled the dash to get to the components. AC works but the revs on the truck is jumping all over the place. Initially upon pickup and puting it in reverse the truck died out. Sometime the revs and tach just jump up and down. Is this something the AC guys could have caused and messed with or is this just a coincendence and something else I need to fix.

Also noticed right under the dash, some plugs that seem to be lose. There is a gray plug end right where the hood latch is that doesn't have anything plugged into it. Also, there is another gray plug with nothing attached next to the plug to hook up the computer.
Are these the cause?

Help please.....