95 Achieva Intermittant stalling-

Greetings!
I recently purchased a 1995 Achieva S-3.1L automatic tranny with 160,000KMs.
It was running great but it now seems to have some issues. It will randomley shut off while driving,then won't start. When this happens,the fuel pump does'nt come on when ignition is turned on,(why it won't start) .Fuel pump will sometimes energize if I run gear shift through P-N-D and back to P , and the engine will start,but When I shift into reverse, the engine will quit. I can hear a high pitched beeping noise coming from the Neutral safety switch on the tranny, under the Brake
master cylinder periodically when this happens. The car seems to reset itself if left for 2-3 hours.
The "check engine light seems to come on before all this happens...
I can't afford to have the codes read right now, and would really appreciate
any ideas...

UPDATE! Finally got to the root of the problem! The wire harness that
runs beneath the air intake( and the throttle cable bracket) was loose.
Whenever it was jolted, it was grounding out and resetting the computer
, ox sensor etc. I have secured the harness, and the car has been working great ever since... this also caused BLACK SOOTY EXHAST,
AS IT WAS MESSING WITH THE SENSORS/ MIXTURE.AS WELL, BEFORE
THE FIX, CAR WOULD START THEN SHUT OFF WHEN PUT IN GEAR....
IF THIS SOUNDS FAMILIAR,MAY WANT TO CHECK THIS BEFORE SPENDING
$$$ ON PARTS YOU MAY NOT NEED.