P2100 is ELECTRONIC THROTTLE CONTROL MOTOR CIRCUIT
Your first diagnostic should be to get your battery load tested to ensure it isn't having a problem.
Your second diagnostic is to check for any signs of a foreign material (ice or dirt) on the Throttle Plate or in the bore causing the Throttle Plate to stick ... make sure everything with this system is connected properly, and all tubes are tight.
Your third diagnostic is going to be a much more involved inspection of the wiring, connectors, and function of two circuits: K124 and K126. Your motor, PCM, or wiring could be bad.
If you find the first two are OK and want to tackle more, let me know.
From the FSM:
When the PCM detects an internal error or a short between the ETC Motor- and ETC Motor + circuits in the
ETC Motor Driver. One trip fault. ETC light is flashing.
NOTE: When this DTC is Active the engine speed, torque, and vehicle speed are limited to a Limp in mode.
NOTE: If the P2100 is intermittent, it is possible that the controller is overheating in extreme hot temperatures,
and this is considered a normal protection operation. No repair is necessary.
NOTE: Low battery voltage can also cause excessive current draw, in very hot and very cold ambient temperatures.
Make sure the battery can pass a load test before continuing.
Look closely at the temperatures at which this DTC set.
THROTTLE PLATE / BORE INSPECTION
(K124) ETC POSITIVE CIRCUIT SHORTED TO BATTERY VOLTAGE
(K126) ETC NEGATIVE CIRCUIT SHORTED TO BATTERY VOLTAGE
(K124) ETC POSITIVE CIRCUIT SHORTED TO THE (K126) ETC NEGATIVE CIRCUIT
(K124) ETC POSITIVE CIRCUIT OPEN
(K124) ETC POSITIVE CIRCUIT SHORTED TO GROUND
(K126) ETC NEGATIVE CIRCUIT OPEN
(K126) ETC NEGATIVE CIRCUIT SHORTED TO GROUND
LOW BATTERY VOLTAGE
ETC MOTOR/THROTTLE BODY
1998 ZJ, 4.0 // 2005 WK Limited, 4.7 // 2008 KK 3.7