Don't believe in stories that ECU can be reset by disconnecting the battery - it is not true.
I'm not sure you're correct there. Below is an old procedure from a Sportsalfa thread some years ago. Supposedly the "working memory" - which contains idle / throttle values etc - can indeed be reset using the below notes. In my case it works, as similar procedures have on others cars I've owned over the years.
BEFORE STARTING: ENSURE THE IGNITION IS OFF AND KEYS REMOVED. ALSO, IF THE RADIO IS CODED MAKE SURE YOU HAVE THE NUMBER.
1. Disconnect the -Ve terminal of the battery for 45 min to let the ECU's 'working' memory clear. The ECU also has a non-volatile memory area where things such as the master keycode, faults and mileage etc. are stored that will not be cleared.
2. Reconnect the -Ve terminal after 45 minutes.
3. Put key into ignition and turn to MAR (don't start the car) for 10 seconds then turn to stop position. During this time DO NOT press the accelerator pedal. This step apparantly lets the ECU read the rest values of the pedal.
4. Start the car but again DO NOT USE OR PRESS the accelerator pedal. Let the car idle for 10 minutes without pressing anything. This step allows the ECU to calibrate the motorised throttle, idle and any other required warmup values.
5. Finally, after 10 minutes drive the car to your nearest favourite 'test track' and as the saying goes "Drive it like you stole it" for a while. This give the ECU a decent baseline for it's trim values matched to the engine and ancilliary components condition (such as a new MAF).
The guy who originally wrote this did extensive research on (iirc) an Alfa GTV P2, he tried various replacement parts without running the above procedure (effectively not reseting the ECU) and noticed significant differences when he did.