You need to establish if your car has a VSS (the speed sensor in the gearbox) or if get's it's road speed info from the ABS.
I assume the latter if you have ABS warning on too. Are you able to scan the ABS?
Throttle position sensor is the sensor on the throttle body, usually a 3 wire job.
Make sure the cable hasn't been adjusted so the throttle isn't closing fully.
P0121
Error Description
Throttle Position (TP) Circuit Performance Problem The TP sensor circuit is monitored by the PCM for a non closed throttle position at idle.
If key ON engine running self-test terminates upon placing the transmission range selector in gear (DRIVE or REVERSE) or when closing the throttle (idle) after opening it (in PARK or NEUTRAL) the TP closed throttle position is not attained, the test fails. Binding throttle linkage Damaged throttle body TP circuit open to PCM Damaged TP sensor SIG RTN circuit open to TP sensor Drive vehicle, bring to a stop, turn key OFF. Start vehicle, run key ON engine running self-test at idle.
Access KOER diagnostic trouble codes on scan tool.
P0500
Error Description
Vehicle Speed Sensor (VSS) Malfunction Indicates the powertrain control module (PCM) detected an error in the vehicle speed information. Vehicle speed data is received from either the vehicle speed sensor (VSS), transfer case speed sensor (TCSS), anti-lock brake system (ABS) control module, generic electronic module (GEM), or central timer module (CTM).
If the engine rpm is above the torque converter stall speed (automatic transmission) and engine load is high, it can be inferred that the vehicle must be moving. If there is insufficient vehicle speed data input, a malfunction is indicated and a DTC is set. On most vehicle applications the malfunction indicator lamp (MIL) will be triggered when this DTC is set. Open in VSS+/VSS- harness circuit.
Open in TCSS signal or TCSS signal return harness circuit. Short to GND in VSS harness circuit. Short to GND in TCSS harness circuit. Short to PWR in VSS harness circuit. Short to PWR in TCSS harness circuit. Open or short in the vehicle speed circuit(s) (VSC) between the PCM and appropriate control module.
Damaged VSS or TCSS. Damaged wheel speed sensors. Damaged wheel speed sensor harness circuits.
Damage in module(s) connected to VSC/VSS circuit. Damage drive mechanism for VSS or TCSS. Monitor VSS PID while driving vehicle. This DTC is set when the PCM detects a sudden loss of vehicle speed signal over a period of time.
If vehicle speed data is lost, check the source of where the vehicle speed input originates from: VSS, TCSS, ABS, GEM or CTM. Note: On some MSOF applications, VSS and TCSS PID can be monitor. However if no TCSS PID is available and VSS PID is zero, TCSS circuitry frequency must be checked for loss of sensor signal.
If another vehicle electronic module has generated the P0500 and the vehicle does not receive its vehicle speed input from one of the above mention sources (VSS, TCSS, ABS, GEM or CTM).
Check the PCM for Output Shaft Speed Sensor (OSS) DTCs.
On OSS applications the PCM uses the OSS to calculated the vehicle speed. If no OSS DTCs are found check for correct PCM configuration.
Check PCM configuration for correct tire size and axle ratio.