Quote:
Originally Posted by chops
you're correct in that the ambient air sensor is mounted in front of the radiator, but what you're not accounting for is that the IAT temperature is taken at the MAF sensor. thats the sensor in your intake tubing just before the throttle body. it is completely normal for the temperature to be higher than the ambient air because the air needs to travel from the intake hole by the radiator all the way up the tubes and measured.
when your car is running, the temperature difference will be significantly higher as there will be some heat soak from your engine
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I understand that the IAT comes from the MAF (located in the filter box outlet) and that, when the engine is running, the air will get heated. When my engine is running the difference between ambient and IAT is at least 9-10F; higher when stopped or moving slow. I am seeing the 6F difference when the engine is cold. Or at least I think it was cold - I will be running another, longer test with fans tonight.
Edit: mentioning that the temp sensor is in the filter box made me realize that it is very easy to get the temp in the duct at the MAF when the engine is not running. I just pulled the filter out and stuck a temp probe next to the MAF. The engine is still quite warm and I have to go out of town this PM. I'll report back later this evening.