Engine Miss/Noise

Howdy guys! I have sort of a strange question. I have a 1996 Lesabre that I bought used. She now has 88,000 mi. When I crank my car a rush of air is heard immediatly following start up. The best I can describe the sound is when a fuel injected car doesnt catch when you first start it and you hear a rush of air back through the throttle body. I have noticed that when the temp is below freezing it usually doesnt make the noise. I did some internet research a while back and came across a man that stated the brake boosted was at fault. I changed my brake booster and noticed that if i start the car with the brake pedel depressed no sound however the moment I let my foot off the pedel it sounds as though a rush of air goes through the throttle body? I have determined that is electrical which is triggered by the release of the brake pedel switch. I have changed all my vac lines, upper intake, TPS, Map sensor, Mass air flow sensor, plugs, wires, coils, ignition module, coolant temp sensor, cam sensor, water pump, trans flush and service. The only thing that I have not changes is the Crank sensor or fuel system parts. The car drives awesome except when it goes into OD, feels as though its got some hesitation. Any ideas are greatly appreciated. I am a student and dont have a small fortune to take to the dealer.

Thanks guys!

David Gogley
Birmingham, AL

I think you may have partialy identified the problem as to your statement about having the brake on and the noise not occuring. There is a checkvalve in the vacuum line of my '94 and the plastic had a hole in it while the vacuum hoses were still OK. I got a replacement check valve off one of the HELP racks at a discount auto supply. If you will connect a small 110 volt vacuum pump to the vacuum system and pull a vacuum with the engine not running you can hear any vacuum leaks.]

where would i purchase a small vac pump? And would i connect it to the service port near the breather box? Are you referring to the check valve on the brake booster? When I purchased the new booster a new valve was included.