What is the reason for the high and low idle speed of the car?

(1) The throttle position sensor idle switch is not turned off.

(2) Idle speed control valve (ISC) failure.

(3) The air inlet pipe leaks.

(4) The fuel injector leaks or is blocked.

(5) The exhaust system is blocked.

Fault diagnosis and elimination

(1) Idle switch is not turned off.

Diagnostic method: Turn on the air conditioner or turn the steering wheel when idling. If the engine speed does not increase, this fault can be proved.

Troubleshooting: Adjust, repair or replace the throttle position sensor.

(2) Idle speed control valve (ISC) failure

Diagnostic method: Check the starting sound of the idle control valve. If there is no starting sound, the idle control valve is faulty.

Troubleshooting: Clean or replace the idle speed control valve, and set the idle speed with a special decoder.

(3) Air leakage in the air inlet pipeline

Diagnosis method: If the intake pipe leaks, it proves that the intake system leaks.

Troubleshooting: Find the leakage, reseal or replace the phase parts.

(4) The fuel injector leaks or is blocked.

Diagnostic method: Check whether the fuel injector is injecting fuel with an external power supply, and measure the fuel injection quantity of the fuel injector. If the fuel injector does not inject fuel or the fuel injection quantity exceeds the standard, the fuel injector is faulty.

Troubleshooting: Clean the injectors and check the fuel injection quantity of each injector to ensure that there is no blockage or leakage.

(5) The exhaust system is blocked

Diagnosis method: acceleration is accompanied by tension, which can be determined as the fault.

Troubleshooting: Replace the three-way catalytic converter.