91 ford taurus

I have a 91 taurus that when started cold it runs rough and engine revs up and down, tried looking for bad vac line but cannot find any, i do not hear any hissing sounds anyway. also when accellerating from a stop the heater starts blowing out the defroster vents,replaced the vac operated control switch in dash but to no avail, looked under dash for bad vac lines but cant find any, just had the a/c retrofitted to r-134a back in july. looked for problem in that area but all seems ok, any suggestions. thanks ken