How to Troubleshoot High Intake Air Temperature Readings in Your Car

Intake Air Temperature (IAT) is a crucial parameter for your car’s engine management system. It measures the temperature of the air entering your engine, allowing the computer to adjust fuel delivery and ignition timing for optimal performance and emissions. If you’ve noticed your car scanning or reporting unusually high intake air temperatures, it’s essential to understand why and how to address it. This article will guide you through understanding normal IAT readings, diagnosing potential issues, and steps you can take to resolve high IAT problems.

Understanding Normal Intake Air Temperature

Ideally, your intake air temperature should be relatively close to the ambient outside air temperature, especially when the car is moving. However, several factors can influence IAT readings, causing them to be higher than expected. In forum discussions among car enthusiasts, like those in the Chrysler 300M community, drivers often compare their IAT readings to understand what’s considered “normal.”

One user, Tony (demark), shared his experience of high IAT readings in his Chrysler 300M. On an 82°F day, his scan tool showed an IAT of around 145°F, while his coolant temperature was about 165°F. He observed that the IAT didn’t change significantly while driving around initially, leading him to believe it might be normal. However, after comparing readings with his wife’s Town and Country, which showed IATs closer to ambient temperature, Tony started questioning the normalcy of his 300M’s readings.

Chrysler 300M Forum Discussion

Image: A screenshot from a car forum discussion, visually representing the community aspect of troubleshooting car issues and comparing experiences.

Experienced forum members like Alex (user97) provided valuable insights, explaining that IAT readings can indeed be higher, especially in stop-and-go traffic or idling conditions. Alex pointed out that IAT is more RPM dependent than coolant temperature and can easily reach 150-160°F in warm weather during such conditions. He also correctly differentiated between engine types and intake manifold designs, emphasizing that comparing IAT readings across different vehicles like a Chrysler 300M and a Town & Country (with different engines) might not be directly comparable.

Symptoms of High Intake Air Temperature

While some increase in IAT is normal, consistently high readings can lead to several issues:

• Warm Engine Starting Problems: As Tony initially experienced, high IAT can contribute to difficulties starting a warm engine. Hotter intake air is less dense, reducing the amount of oxygen available for combustion, which can make starting harder.
• Reduced Engine Performance: High IAT can decrease engine power. The engine control unit (ECU) will often retard ignition timing to prevent knocking or detonation when IAT is high, which results in reduced performance.
• Decreased Fuel Efficiency: Hotter air is less dense, meaning the engine needs to work harder to draw in the same amount of oxygen. This can slightly decrease fuel economy.
• Potential for Engine Damage: In extreme cases, prolonged operation with very high IAT can contribute to engine overheating and potential damage if the ECU’s compensations are insufficient.

Potential Causes of High IAT Readings

If your car consistently scans or reports high intake air temperatures, consider these potential causes:

1. Normal Heat Soak: As explained by Alex in the forum, IAT can rise significantly when the car is idling or in slow traffic, especially after the engine has reached operating temperature. This is due to “heat soak” from the engine bay, where heat radiates from the engine and other hot components, warming the intake air ducting and sensor. This is often considered normal within a certain range above ambient temperature.

2. Faulty IAT Sensor: While less likely, the IAT sensor itself could be malfunctioning and providing inaccurate high readings. Sensors can degrade over time or become damaged.

3. Intake System Issues: Problems within the air intake system can lead to elevated IAT:

   • Restricted Airflow: A clogged air filter or obstructions in the intake ducting can reduce airflow, causing heat to build up around the sensor.
   • Heat Sources Near Intake: If the intake ducting is routed too close to hot engine components or exhaust manifolds, it can draw in pre-heated air, increasing IAT.
   • Damaged or Missing Heat Shielding: Heat shields are designed to protect the intake system from engine heat. If these are damaged or missing, it can lead to higher IAT.

4. Sensor Location and Type: As discussed in the forum, the location and type of IAT sensor can vary between car models and years. In older models, the IAT sensor might be integrated with the Manifold Absolute Pressure (MAP) sensor, and its readings can be influenced by its proximity to the intake manifold. Understanding your car’s specific sensor setup is important for accurate diagnosis.

How to Investigate and Reduce High IAT

Here’s a step-by-step approach to investigate and potentially reduce high intake air temperature readings:

1. Monitor IAT Readings: Use a scan tool to monitor your car’s IAT readings under various driving conditions:

   • Cold Start: Note the IAT reading when the engine is cold. It should be close to ambient temperature.
   • Idling/Stop-and-Go Traffic: Observe how high the IAT climbs in these conditions.
   • Highway Driving: Check the IAT at highway speeds with good airflow. It should drop closer to ambient temperature.
   • After Engine Shut-off: Note how quickly the IAT rises after turning off the engine. As Alex mentioned, IAT will increase after shutoff due to heat soak.

2. Compare to Ambient Temperature: Compare your IAT readings to the actual ambient temperature. A significant and persistent difference, especially during driving at speed, might indicate an issue.

3. Inspect the Air Intake System:

   • Air Filter: Check and replace your air filter if it’s dirty or clogged.
   • Intake Ducting: Examine the intake ducts for any obstructions, damage, or if they are routed too close to hot engine parts. Ensure all connections are secure and there are no air leaks before the sensor.
   • Heat Shields: Verify that heat shields around the intake system are in place and in good condition.

4. Check IAT Sensor Wiring and Connections: Inspect the wiring and connector to the IAT sensor for any damage, corrosion, or loose connections.

5. Test or Replace IAT Sensor: If you suspect a faulty sensor, you can try:

   • Sensor Resistance Check: Use a multimeter to check the sensor’s resistance against the manufacturer’s specifications for different temperatures (if available).
   • Sensor Replacement: Replacing the IAT sensor is often a relatively inexpensive and straightforward DIY task. Ensure you get the correct sensor for your car model and year. For older vehicles where the IAT is integrated with the MAP sensor, replacement might be more complex and costly.

6. Consider Intake System Modifications (with Caution): In some cases, improving the intake system’s insulation or routing it away from heat sources can help reduce IAT. However, any modifications should be done carefully and with consideration for proper engine operation and sensor readings.

Conclusion

High intake air temperature readings can be a concern, potentially affecting engine performance and starting. Understanding what constitutes normal IAT for your vehicle and systematically investigating potential causes is key to resolving the issue. By monitoring your IAT, inspecting your intake system, and considering sensor health, you can effectively troubleshoot and address high IAT problems, ensuring your engine receives cooler, denser air for optimal operation. If you’re unsure about any of these steps or experience persistent high IAT readings, it’s always recommended to consult a qualified mechanic for professional diagnosis and repair.