Hi all,
Have a 91 350 tpi. it shudders when it has no load ie: nuetral, rev, or light throttle cruising, but still hickups when parked in gear. When I step on it or put in under load it runs perfect and has tons of power.

Recently it started a new trick, it dies when I put into gear from park sometimes. I have replaced and checked lots of stuff, ranging from ICM to plugs, wires, cap rotor, injectors, good fuel pressure etc. I have no service enging light.

Any ideas are appreciated.

 

Not much to go on, but I'm guessing a significant vacuum leak. Vacuum leaks cause the most havoc when manifold vacuum is high (idling, light load).