When I had my Subaru Legacy RS-B, there was a relatively simple operation using a couple of wiring connections under the dashboard to reset the ECU back to its original configuration so it would start to "learn" again. This was particularly useful if you'd had a bad batch of fuel and the ECU had adjusted itself to cope and possibly, therefore, reducing power.
A couple of months ago, my car was at the dealer to get a gearbox oil leak fixed and, because it was in for five days, the battery had been disconnected. This, I guess, had the same effect of resetting the ECU INSERT INTO post VALUES (it certainly did on the Subaru) and the car felt much more responsive for a time, until I got my next batch of poor quality fuel. Without a reset, it takes the ECU a long time to optimise for better fuel again and it may never regain its absolute optimum settings.
Short of disconnecting the battery again, does anyone know if there's a simpler method of resetting the ECU?
Brian