check your PCV system, hose to valve not sucking flat, freah air path (i.e. breather type cap or air tube to air cleaner). still sounds like vacuum related to me. Does this have a decel valve (valve has one 3/8" hose to manifold, on 3/8" hose to air cleaner & a smaller vacuum hose to a vacuum source. opens up under high vacuum for a short time to lean out under full decel)?
