If you have no vacuum pump then this could also be a problem? have you checked the check valve going to the HVAC hose from the manifold? If you are using the HVAC system and the check valve is bad then you hve a real problem!! When the manifold is as idle there is lots of vacuum. When running though the manifold is coming under boost. This can cause pressure on the HVAC system and cause damage. Big differance between 15 hg of vacuum and 6 lbs of boost! When under boost the vacuum pump kicks in and controls HVAC system. Check is there to insure that no vacuum can escape back into the manifold.

AFM's just do not suddenly get out of adjustment. you should exhaust all all other things first before going there. To do that job properly you need an exhaust gas anylizer to be sure of you idle mixture ratio. With this you could also adjust the idle mixture screw on the AFM.This could smooth out your idle and put you on the right path to fix the RPM hunting on the road.

Jon