I have a 1991 5.0 V8 TBI, it stalls when I go from Park to Reverse/Drive. If I feather the accelerator into gear, it will run fine. Feels as if the idle is set too low, but I since set the timing to spec.
I since changed the MAP, IAC, spark plugs, EGR, Temp sensor, ECM, TPS, Cap, and Rotor to no avail. My friend has suggested replacing the fuel pump and injectors.

 

vacuum leak.

 

I agree. get a can of carb cleaner and spray around vacumm hoses until erradic idle happens.

 

Clean the throttle body if no differance Then look into changeing the injectors ! Those spider packs are famouse for leaking .

 

I also have a 1991 5.0 V8 TBI, that stalls when I go from Park to Reverse/Drive no matter what i do replaced the torque converter and lock up switch next is the tps hope that works