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121 Closed throttle voltage higher or lower than expected
or 121 Indicates throttle position voltage inconsistent with the MAF sensor
122 Throttle Position (TP) sensor circuit below minimum voltage
212 Loss of Ignition Diagnostic Monitor (IDM) input to PCM/SPOUT circuit grounded
214 Cylinder Identification (CID) circuit failure
656 Torque Converter Clutch continuous slip error
I'd start by checking the Throttle Position Sensor (TPS) to make sure it responds linearly, and that the throttle plate is able to fully close when your foot is off the accelerator.
The cylinder identification code could be due to the camshaft position (CMP) sensor or possibly the Crankshaft Position (CKP) sensor. The CKP sensor is a common item to fail when the water pump leaks and will cause a no start or intermittent stalling when it fails on the Gen 1 and Gen 2 SHO engines.
-Rod