Is your Defrost, heater or vents on and the fan in on position? if so turn it all to off then try starting it mine did the same thing The heat/air system works off of vacuum so if it`s on it will do that. It could be the gasket they are known for going bad I replaced mine not to long ago. I used the kit from Huges Engines. It`s realy not to bad of a job to do as long as you take your time.