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2000 Mazda Protege 1.6L MT: Surging/Hesitation at Warm Idle with P0123 Throttle Position Sensor Circuit 'A' High

Model: 2000 mazda protege Fault Code: P0123 Posted: 2012-05-30 21:26

I own a 2000 Mazda Protege 1.6L manual transmission model with 145,000 miles. The car exhibits steady but high idle when cold (ranging from 1500 to 2000 RPM), which gradually settles down after a few minutes of operation. However, once the engine reaches normal operating temperature, I experience noticeable hesitation and surging—particularly during light to medium throttle applications such as gradual acceleration or steady pedal pressure. The issue does not occur at high throttle (3/4 to full throttle). I previously replaced the Mass Airflow (MAF) sensor with a new one and cleared the fault codes, but symptoms persist. After rechecking, I now see a persistent P0123 code: 'Throttle Position Sensor/switch A circuit high'. I have since replaced the Throttle Position Sensor (TPS), yet the problem remains unchanged. Two weeks ago, I also performed a full ignition system overhaul—replacing spark plugs, wires, and coils—to rule out any ignition-related issues. No vacuum leaks were detected during inspection; spraying starting fluid around the intake manifold gasket showed no improvement in idle or visible leaks. The behavior is consistent: the car runs smoothly when cold but begins to hesitate/surge precisely as engine temperature reaches normal operating levels. The wiring harness from the TPS appears intact, and I’ve checked all connections. My next step is to measure voltage at the TPS harness, trace the wires back to the ECU (Powertrain Control Module), and inspect for any shorts or poor electrical connections. Any additional insights or troubleshooting tips would be greatly appreciated.

Related fault codes

P0123

Comments (3)

Anonymous 2012-06-05 13:33

A 'high' reading in Sensor Circuit A indicates an open circuit on the sensor input wire 'A'. Check the resistance of the wire from the TPS to the ECU (PCM)—it should read less than 5 ohms for proper continuity.

Anonymous 2012-08-18 17:16

My Mazda also displayed a P0123 code, accompanied by symptoms like transmission dropping from third to second gear prematurely and a flashing overdrive light. The root cause was a corroded positive battery terminal that reduced voltage delivery to the Throttle Control Body (TCB) down to only 0.8 volts. Despite all other systems functioning normally, the TCB received insufficient power. This issue was identified through DaveJHM’s post at: http://repairpal.com/over-drive-light-broken-po123-084. After resolving the battery terminal corrosion and restoring proper voltage, the P0123 code cleared. Note: A few days later, I experienced new transmission-related codes—either P1102 (MAF signal inconsistent with TPS) or P1121 (TPS signal not consistent with MAF), along with either P1122 (TPS stuck closed) or P1123 (TPS stuck open). However, I believe the throttle was never actually stuck. Replacing the TPS resolved all these issues. Before replacement, I tested both old and new TPS units—measuring resistance across combinations (A-C, B-C, A-B)—and found the original unit had slightly lower resistance in each configuration.

Anonymous 2012-09-04 21:19

I would also like to add that after fixing the voltage issue, my car developed new transmission-related codes: either P1102 or P1121 (inconsistent TPS/MAF signal), and either P1122 or P1123 (TPS stuck open or closed). However, I believe the throttle was never physically stuck. Replacing the Throttle Position Sensor completely eliminated these symptoms. Before replacement, I compared resistance values between the old and new TPS units—old unit showed slightly lower resistance in all combinations (A-B, A-C, B-C), suggesting possible sensor degradation.