One more thought- I have a friend who had a similar problem a few years back. Turns out they were letting their car warm up for 20 mins a day in the winter and didn't take that into account.

it don't matter what time of year my car doesn't sit and warm up...if it is really cold then i might let it idle for about a minute to allow stuff to start circulating...there is really no point in letting it warm up as if you drive it mine only takes about 1-2 minutes before it is blowing warm air and about 5 or 6 to be at operating temperature

I wait until my car goes into closed loop

I also warm up the car all the time before i go , i always wait for the rpm to drop near 1000 rpm before leaving
It may not help much on gas mileage but even then on highway a see my gauge go down one notch at every 15-20km done at cruising speed of 110-115km/h so gas goes by pretty fast

Ok I figure I will bring back this thread since it is somewhat related and I don't feel like adding new threads...for a while now (since about mid-september) my car has been showing steady declines in fuel mileage, it has also been pulling higher rpm to hold speed than normal, though I can coax it to drop for a while and sometimes if I go straight to the highway after a particular bout of being racy (lots of hard quick acceleration with no speed maintenance) it will do it on it's own until the next time I shut it off. I have log files that I took using torque that I will add in, I highlighted in yellow going 80 down the interstate, in green an area during that time when I made it shift to the right rpm for a bit, and in red a quick 80-100 pull to show what it did under stress (I was very alone at the time) I hadn't realized until afterwords that it was set to record every second so it is a long file and that is part of why I picked it apart. The first highlighting is on line 456, I left it all there to see if there was anything else that might help outside of it, at the end of the log I was sitting idle

https://drive.google.com/file/d/0B_n...it?usp=sharing

bump