Actually, depending on the year some comuters do learn. They have a set map they use as a starting point,but they also have the capability to learn and store "driving habits" as we called it.
It retains this in flash memory like pc ,but like a pc if the backup battery goes dead then you need to reconfigure bios.
The ecu will just go back to stock mapping ,which will not make it run that bad. My guess would be fuel contamination and possible injectors being clogged. Maybe even plugg wires have been eaten by mice or field rats.
But in no way what so ever will unplugging the ecu cause any vehicle not to start up again one it is reinstalled. In most cars you will not notice any difference,if that were the case how could we possibly replace batteries and alternators. Just not true.
We do see learning curves start from scratch and the mpg meters in the trip computers and onboard displays go back to a base mpg reading ,like from 18mpg to 15mpg until it runs a tank or 2 through it. That and fuel economy may be affected ,by relearning the octane and ping signals from both knock sensors and o2 sensors and air temp ,and all the other sensors.
We saw this with what we called winter gas out here in Ca in 90-91 when peoples fuel mileage went doen from 21 around town in a LS400 Lexus to 15mpg. That was caused by the alcohol and the MTB's put in the gas to make it oxygenated. Which in a older car without o2 sensors fore and aft of the convertors and the ecu controlling cylinder like we have in some cars would make it run cleaner and hotter when cold. But in these high end cars it made the ecu think it was runing to lean, which made it richen it up .that ate up gas like crazy,so how did we save the enviroment by using more gas and putting more pollutants into the air...
we didnt... but i aint on the Air Resources Board for that arguement.
In short i beleive the ecu isnt the problem in your friends case,chek the basics first fuel and spark .Run some fuel system cleaner through it and change the plugs if need be.
Good luck
GGary
