97 civic hatch b18c vtec with 95 p28 ecu was ckecking mis fire problem , unplugged map & started it forgetting about it being unplugged cel came on ,replug sensor tried to clear w/back up fuse code 3 & cel stays on . have 5v at sensor ,ground wire gd 0 ohms but pcm signal is 4.98v running or not key on. same readings at ecu . why getting 5v on signal wire and no change w/ vacume? thinking bad map ,but no CEL before unplugging it.