92 cavalier died

I have a 92 cavalier with a 2.2 auto and i left it running when i went into the store and came back out got in stepped on the brake and put into reverse and it died and did not start bake up. It crank with no problems. all fuses are good. ran codes and came back with code 66. depending what site i got its ether the a/c or ecm. a little more help would be appreciated.