1. Common problems of the Renault series: Poor plug contact (the most common cause)
For the Renault models of that period, the wiring harness plug connecting to the throttle (loose or oxidized plug spring) was a well-known design defect.Symptom: Even if a brand-new throttle is installed, due to poor plug contact, the ECU still cannot receive the correct resistance signal, and will directly report P0120, causing the engine speed to fluctuate (even stalling at 2000 rpm).
Solution: Disconnect the battery, remove the throttle plug, and clean the plug pins with electronic contact cleaner (WD-40 green can). Check if the metal spring inside the plug is loose. If necessary, slightly tighten the spring with a fine needle or directly cut off the old plug and replace it with an improved wiring harness plug repair kit.
2. Failure to perform "computer adaptive learning" (initialization)
The internal resistance value of the new electronic throttle is different from that of the old part, and the car computer (ECU) has not been calibrated, which will lead to control disorder and unstable engine speed.
Renault manual initialization method (try without computer when available):
Pull out the key / turn off the ignition switch, wait for 30 seconds.
Insert the key and turn it to the ON position (the dashboard lights up, but the engine does not start).
Keep the ON position for at least 30 seconds (at this time, carefully listen to the engine compartment, the throttle motor will emit "clicking" self-check and seeking limit point sounds).
Turn off the ignition switch, wait for 10 seconds.
Restart the engine and let it idle at the original speed until the water temperature is normal.
Professional equipment: If manual fails, it is necessary to use Renault专用 diagnostic computer (Renault CLIP) or universal diagnostic instrument to enter the engine control unit and perform "throttle adaptive reset/setting".
3. Leakage of intake manifold/base
The intake manifold and throttle base of the Renault 1.2L/1.6L engine have rubber sealing rings.
If the sealing ring is displaced or deformed when installing the new throttle， or if the plastic pipe of the intake manifold has cracks， it will cause a large amount of external air to enter the engine without being calculated by the throttle， thereby causing severe idle fluctuations and instability.
4. Check throttle pedal sensor (TPS)
The definition of the P0120 fault code also covers "throttle pedal". For some Renault models， the throttle pedal sensor wiring harness and the engine compartment wiring harness have a relay plug above the driver's foot pedal. If it is damp or has poor contact there， it will also simultaneously trigger P0120 and cause the throttle to malfunction.