When the engine runs at low idle, the temperature of an exhaust manifold port can indicate the condition of a fuel injection nozzle.
A low temperature indicates that no fuel is flowing to the cylinder. An inoperative fuel injection nozzle or a problem with the fuel injection pump could cause this low temperature.
A high temperature can indicate that too much fuel is flowing to the cylinder. A malfunctioning fuel injection nozzle could cause this high temperature.
Use the 349-4201 Infrared Thermometer to check this exhaust temperature.