Originally Posted by thom52
It does look like the computer "diagnostic" hookup, did something to the car, IMPROVING overall gas mileage. Still not exactly kicking up my heels about its ACTUAL "City" mileage, but at least I can see some hope now of the ever increasing time they are asking for mileage break-in, and "summer gas" getting us into reasonable "mixed" mileage and awesome Freeway mileage.
It could be that a side effect of the "diagnostic" was to reset the ecu. This clears learned parameters and allows the car to relearn with a clean slate. It could be that reseting allowed the ecu to begin relearning in conditions it was more likely to face on a daily basis rather than what ever conditions it was subjected to out of the factory. Anyone can reset the ecu simply by disconnecting the battery. Please note: radio presets will also be cleared.