This is about my 2001 Acura MDX (J35 motor). I have always noticed and wondered, but never asked, why does this car perform best around 70 degree outdoor temperature. +/- 4-5 degrees. Its very noticeable. Throttle response and acceleration is much better between approx. 67-74. Why is that ? If the ecm is always maintaining a constant air:fuel ratio then what would cause this obvious difference in performance ? I have owned this car for almost 15 years so I know this is not about difference in fuel or location/altitude or load in the car and this has happened all along.
Is this normal ? or is something not working properly ?

 

Is that the coolest weather you typically find? Cool air is more dense and you can make more power with cool air vs warm air. Your fuel economy will sag as a result of that extra power too. Perhaps not noticeably though.

 

No that's not the coolest. It can go down to 50° or even in the 40s sometimes. And at those temperature extremes (much colder or hotter than 70°) it does not perform the same way it does at 70°. In fact at 40 or 90 it would be quite worse.

 

Well, so much for that idea.

 

If the denser air theory is true then all cars would always perform better below 70 or 60 degrees and worse above 70 or 80 degrees but generally they dont.. My MDX performs worse either way, except in one narrow band of temperature, and seems like no one else has had a similar experience, so thats why I think something's not quite right. Maybe the intake temp sensor is not accurate or the pcm is not processing it properly..