Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
When you start your car in the morning, the engine runs faster than it should for a short time. It's like when you wake up and start running too fast before you're fully awake.
The engine control module (ECM) has detected that the idle speed during a cold start is higher than the expected range for Bank 2.
The P158F code indicates that the ECM has found the idle air control system to allow more air than necessary during a cold start, causing the engine RPM to be higher than expected on Bank 2. This could be due to a malfunctioning idle air control valve, vacuum leak, or other related issues.
• Higher than normal idle RPM during cold start
• Check Engine Light illuminated
• Rough idle
• Faulty idle air control valve
• Vacuum leak in the intake system
• Faulty throttle body
ECM: Engine Control Module
RPM: Revolutions Per Minute
• Check for vacuum leaks in the intake system.
• Inspect the idle air control valve for proper operation.
• Examine the throttle body for dirt or obstruction.
• Replace or clean the idle air control valve.
• Repair any vacuum leaks found in the intake system.
• Clean the throttle body and ensure proper operation.
• OBD-II scanner
• Vacuum gauge
• Throttle body cleaner
$100 - $300
Moderate
• BMW 3 Series
• Audi A4
• Mercedes-Benz C-Class
• Regularly clean the throttle body.
• Check and maintain vacuum lines.
• Perform routine engine maintenance.
Engine Performance
• Do not ignore the Check Engine Light.
• Have your vehicle inspected by a professional if symptoms persist.
Check with your vehicle manufacturer for warranty coverage on emission-related components.
This code commonly appears in vehicles with higher mileage or those that have not been maintained regularly.
Moderate – While the vehicle may still operate, it can lead to increased fuel consumption and emissions.
Driving with this code may not be compliant with emissions regulations in some areas.
• Engine must be cold.
• Vehicle must be started after sitting for several hours.
The idle air control valve is typically located on the throttle body of the engine.
Q: Can I drive with a P158F code?
A: Yes, but it's recommended to address the issue as it can affect fuel efficiency and emissions.
Q: How can I prevent this code from appearing?
A: Regular maintenance, including cleaning the throttle body and checking for vacuum leaks, can help prevent this issue.
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