Idle Problem

My 1989 Ford F250 7.5/460 Has A Severe Idle Drop From 1000rpm To 450prm When The Trans Is Changed From Drive Or Reverse To Neutral And/or Park. Engine Will Almost Stall. I Replaced Map Sensor And Iac Motor. New Plug/wires/dist Cap/rotor/pcv Valve In Tune Up. Truck Has Either 47,000 Or 147,000. Hard To Tell Since I Bought It Used From A Dealership. Does This Both With And Without A/c On. Does Anyone Have Any Idea What This Could Be Caused By? Thanks In Advance

Check your fuel pressure, you might have low enough fuel pressure that the fuel is not atomizing proporly when coming out of the injectors. My chebbie is starting to do the same thing. It has 10 psi lower fuel pressure than what it is supposed to, and it has little power and poor fuel milage.

Chevyman, I Replaced The Fuel Filter Today And Lo And Behold My Problem Stopped. Everything Seemed To Be Better. Better Pickup, Smoother Idle, And Quicker Starting. She Purrs Like A Tiger Now. By The Way, After I Installed The Pump And Reset The Fuel Inertia Switch, She Cranked But The Battery Suddenly Died (4 Years Old). Some Coincidence. Anyway, I Replaced The Battery With A New One And I'm Good To Go. Thanks Man