Fuel economy changes far too much with the wind and the weather, the seasonal blends of fuel, different traffic around you, regional differences with more or less hills, elevation, different paths you take on your errands, etc. to use it as any kind of genuine measuring stick for a problem. It *might* give you a hint but you have to be supremely good at salting your data you are collecting and mentally offsetting it against the many continuously changing driving conditions. Most people are not capable of that (although they will think they are), and you don't want to get people thinking they can use fuel average guesstimates from the computer as indications of whether all is right with their car. You are going to end up with people who think they have problems coming and going every other tank because that tank average went up or down 2-3 MPG. I mean, come on, we can barely keep up with explaining to people that they have to manually reset the fuel average after each fillup.
People come on here and throw out their problems and try to use their fuel economy as evidence or symptoms of their problems all the time. I flat-out ignore anything anyone tells me that they have determined based on a couple of tanks of fuel in who knows what driving conditions. Its completely useless extra unrelated data.
I appreciate the advice.
You are right, it is difficult to prove, especially considering the lack of consistency in driving overall. You never know when you are going to hit a traffic jam.
However, I am generally cognizant of how quickly the throttle responds, and I can say that there is a significant difference between the throttle with traction control off and traction control on, and that over a driving period you can really see the difference in gentle driving conditions in how fuel economy is affected by traction control.
For me, I started out at about 23.4-23.9, with mixed driving.
Over time, fuel economy rose to about 24.2.
After I started turning off TSC, it rose to 24.7 - this is for the main, overall, since purchase fuel consumption average.
I also reset my gauge, and it reads between 25 and 27 MPG, depending on the balance of road driving for the period. Some of that is just due to the engine being broken in, but more of it is due to the traction control, especially with the timing of the changes.