Hyundai Santro Idle RPM Fluctuation Problem

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Hyundai Santro Idle RPM Fluctuation Problem

Many Hyundai Santro owners in Pakistan complain about unstable idle RPM, especially when the AC is turned on o r during cold starts. What are the main causes of this idle fluctuation, and which parts should be checked first to diagnose the issue?

Talha Kyanii asked on 03 Dec 2025 14:18:49 pm

1 Answer

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Talha Kyanii - on 03 Dec 2025 14:21:57 pm

Idle fluctuation is one of the most frequent issues in Santro, especially older models. It usually happens due to:

Common Causes

Dirty o r faulty IAC Idle Air Control valve
The IAC controls engine idle. When it gets dirty, RPM goes up and down.

Throttle body carbon buildup
Carbon deposits disturb airflow and confuse sensors.

Weak o r leaking vacuum pipes
Cracked rubber pipes cause air leakage, affecting idle stability.

Faulty MAP sensor
Gives incorrect air-pressure readings to the ECU.

CNG tuning issues
Poorly tuned CNG often causes idle fluctuation when switching AC on.

How to Fix

Get throttle body service and clean the IAC valve.

Replace damaged vacuum pipes a very common issue in older Santros.

Have a mechanic check and clean the MAP sensor.

Tune CNG properly if the car is dual-fuel.

Make sure the engine is not running on weak ignition coils o r plugs.