My 99 ford windstar is pulsating while stopped at a light

The mass air flow sensor, the throttle body and the idle air control motor need a good cleaning. Use a brush and brake clean everything except the Mass air flow sensor, just spray it down, both sides. After you clean it, it will take a few second to restart.

this because when in gear there is drag.... there isn't when u are in park u need to adjust ur idle to about 750-800

How long has this been going on? When a problem like this develops, it's always a good start to check for any fault codes in your engine's computer. Autozone and a few others will do a scan for free and give you any code numbers and technical descriptions, if the computer has stored any faults.
If you've kept track of normal maintenance over time, then a low idle should be a fairly easy problem to fix. That being said, it's not so simple. The computer controls your idle speed under all conditions, and relies on several sensors and switches (inputs and out puts) to work effectively. Have your mechanic check it with the low idle, dying problem in mind. Sounds to me like it needs tweaking-idle control valve, throttle position sensor, air flow meter. See? Get the proper diagnosis, so you don't buy unnecessary parts.
Maybe our ford guru, emissionwiz, will stroll along and find your fix from memory (he's the best).

I have a 98 Windstar and it would die when pulling up to a stop sign, slowing when coming to a stop or making a slow turn. According to Ford recall 98E03 EMISSIONS RECALL some vehicles may stall during deceleration when coming to a stop, during slow speed parking maneuvers and/or coasting thru slow sweeping turns. This may be caused by the Powertrain Contro lModule (PCM) calibration dropping the rpms too quickly during deceleration. This involves reprograming the PCM. The revised calibration will allow the engine rpms to drop slowly during low speed maneuvers to reduce the possibility of a stall. Call your local FORD dealership (have your VIN handy) and have them check to see if this recall has been performed on your vehicle.

it sounds like its drawing air into the inlet mannifold

clean the MAF sensor first and also add some Chevron Techron fuel injector cleaner to 1/4 tank of gas. You may have a dirty MAF or a partially plugged injector.

block off vacuum hose to brake booster and see if idle returns to normal if it does you need new brake booster has hole in diaphram internally some times slight hissing noise is evident in cab when pressing brake pedal to section where engine surges or idles high. also check for fuel leaks from hoses if you can smell fuel in engine bay while running and engine warm some leaks only leak while running and hot

check the swiches at the brake pedal their should be two. one for brake lights and one for transmission dump valve it prevents the engine from loading up at lower rpm. ie stoping at lights while in drive

is there a hissing sound when depressing the brake pedal.

You maybe need to adjust the idle speed, on top of the intake manifold, near where it says EFI, there a small black rubber plug, pull it out, turn off everything in the car, then turn the screw in where the plug was to change the idle speed. Or it could be that you need a new Idle Control Valve