My highway mileage is great but I have a big problem in the city. The main problem is when the car is idling. Can someone please tell me if they have the same make and model if they are idling with the A/C on do they lose 1/10 of a mpg for every like 30 seconds or so. In 5 min the car loses like 1 mpg and in 50 min like 10 mpg. My MPG went from 20 to 10 in just 50 minutes of the car idling with the A/C on.

 

Saw there was no reply. MPG loss like crazy when idle is normal. MPG is Miles/Gallon. It take gas to run everything so the denominator gets bigger, and you are not moving so the numerator stays the same. This is why the stop/start technology to turn the motor off at stops etc was rolled out on MINI and possibly other makes.

 

the computer does not care if you are driving or sitting at idle, all it does is calculate fuel used compared to the driving. If you do not want to have low ratio, turn off the car and the MPG will not drop like you are experiencing.