1992 Olds Cutlass mileage: 154,000. My wifes car is surging (lunging) at idle and when coming to a stop. It sometimes thinks its in third gear and stalls when coming to a stop after an extended ride (25 mi.). This is an intermittent condition. I had a friend put it on the computer and there were no trouble codes. He said it might be a transmission sensor.
Your car has a lock-up torque converter in the transmission. It locks-up only in high gear. It is supposed to disengage at lower speeds. Yours is not disengaging. There is probably a valve in the transmission hanging up . Having the transmission serviced with new fluid may help the problem. Next step, the valve body will have to be removed and cleaned.