Hi Euromodder
I looked into this idea myself a month or so ago and didn't have much success due to my car's age and I wanted to do it myself so I could continue to tune the best parameters
The thread I started is here. It has some good responses
http://ecomodder.com/forum/showthrea...ion-13824.html
The concept is definitely a good idea, the ECU configuration and design for the whole car is set up for the worst case conditions and some things are set up for drivability at the expense of wasted fuel.
Unfortunately the implementation can be difficult. For my car in particular I have a car that doesn't have the programming connection instead it has inbuilt configuration values. From what I have read you can usually change out the eeprom or connect up a daughter board which will override settings but I personally wasn't willing to spend that much on the modification and there is a risk of killing your car completely so if your doing it yourself I highly recommend getting a second ECU from a wrecker or something like that.
If your getting a chip tuning place to do the work for you there is the disadvantage of you might not understand what they are tuning out so you may not get the best efficiency or they might cause damage to the car (running too hot or something like that)
You can also go down the path of replacing your whole ECU with a customizable version which is often done in racing however it can cost a lot of money for a customizable ECU.
If you have a bit of a search on google you will find some chip tuning web sites and instructions which might help.
As for my solution I will just be "fooling" the ECU by either overriding its outputs or changing its inputs so it does what I want.
Good luck.