How do you set the cold start idle speed on a Hyundai atoz G4HC Engine?

You can't directly set the cold start idle speed on a Hyundai Atoz (G4HC engine) like you might on older carbureted engines with a screw adjustment. The idle speed is controlled electronically by the Engine Control Unit (ECU). The ECU uses various sensors (like the intake air temperature sensor, throttle position sensor, and coolant temperature sensor) to determine the appropriate idle speed for different conditions, including cold starts.

If your Atoz is experiencing a problem with cold start idle speed (e.g., stalling, excessively high or low idle), it's not something you adjust manually. The issue likely stems from one of these possibilities:

* Faulty sensor: A malfunctioning sensor (e.g., IAT, CTS, TPS) will provide inaccurate data to the ECU, leading to incorrect idle speed control.

* Dirty throttle body: A dirty throttle body can impede airflow, affecting idle. Cleaning it might resolve the issue.

* Vacuum leaks: Leaks in the vacuum system can disrupt the engine's idle control.

* ECU problem: A faulty ECU is a less common but possible cause.

* IAC valve (Idle Air Control Valve) problem: This valve regulates air bypassing the throttle to control idle. A dirty or malfunctioning IAC valve is a likely culprit.

Instead of trying to adjust the idle speed yourself, you should:

1. Check the obvious: Ensure the battery is properly charged and the air filter is clean.

2. Have a professional diagnose the problem: Take your Atoz to a qualified mechanic or Hyundai dealership. They have the diagnostic equipment (OBD-II scanner) to check for error codes and identify the faulty component. They can then repair or replace the necessary parts. Attempting to adjust something you don't understand could damage the engine or other components.

Trying to manually adjust the idle speed on a modern electronic fuel-injected engine is highly discouraged and unlikely to yield positive results. Professional diagnosis and repair are the best approach.