If your 300M's idle speed is too high or too low, it's not a simple adjustment. The problem lies *elsewhere* in the system. Here's what you should do:
1. Check for diagnostic trouble codes (DTCs): Use an OBD-II scanner to read any trouble codes stored in the PCM. These codes will pinpoint potential issues that could be affecting the idle speed. Common causes include:
* Faulty Idle Air Control (IAC) valve: This valve regulates the amount of air entering the engine at idle. A malfunctioning IAC valve is a very common cause of erratic idle.
* Dirty or faulty Mass Airflow Sensor (MAF) sensor: This sensor measures the amount of air entering the engine. A dirty or malfunctioning MAF sensor provides incorrect information to the PCM, leading to improper idle speed adjustment.
* Vacuum leaks: Leaks in the intake manifold or vacuum lines can drastically affect the idle.
* Throttle body issues: A dirty or sticking throttle body can also cause problems.
* Faulty PCM: In rare cases, the PCM itself may be faulty.
2. Address the DTCs: Once you have the codes, research their meaning and address the underlying problem. This often involves cleaning or replacing the faulty component (IAC valve, MAF sensor, etc.). A vacuum leak might require careful inspection and repair of hoses and gaskets. A dirty throttle body usually requires cleaning with throttle body cleaner.
3. Professional Help: If you're not comfortable diagnosing and repairing automotive electrical and mechanical systems, take your 300M to a qualified mechanic. They have the tools and expertise to diagnose and fix the problem correctly. Attempting to adjust the idle speed directly (if even possible) without understanding the root cause could lead to further damage.
In short: Don't try to manually adjust the idle speed. Focus on diagnosing and fixing the underlying cause indicated by any trouble codes.
