OK, it sounds like the tether connections to the motor may be bad. The chuffing is based on motor voltage. If there is no motor load, when you apply power, it'll chuff like crazy but not go anywhere.
First step is to check the solder joints on the locomotive tether PCB, they frequently break free. A little solder and the touch of the iron will fix that. The other tether issue is a wire breaks right at the connector from the tender, that requires a new 4-pin tether. The good news is, many of us have tons of them left over from command upgrades.