as i have done a search with no luck, i am wondering does anybody have information as to why the (manual) ac/heater control vacuum would fluctuate in relation with acceleration? under acceleration, the blend doors operate with out touching the controls. i have already replaced the defrost/register vacuum motor (part # yh451) probably due to pre-mature failure because of the constant cycling. i also found a (broken/rotted apart) vacuum line that disappears down the passenger fender, with no luck in finding where the other end is. does anyone know where that goes to? thanks to everyone!, especially shorod!

If you're comfortable that you don't still have a vacuum leak somewhere, you should make sure the check valve for the HVAC vacuum is installed and working, as well as the HVAC vacuum tank. From the diagram I found in the service manual, it appears the check valve and tank are located in the engine compartment rather than the passenger compartment.

Does your car still have the vacuum diagram sticker under the hood which may help you track down the vacuum line on the passenger side?

-Rod