It just gets worse and worse. Wekk here it goes, I hope this covers all the helpful suggestions and fixes that were posted by everyone out there in Alfa land.
First off, I have two standard keys and the master key, I bought the car from new in 1996 and did not lose any keys.
As the keycode unit was not reading the keys (code light on dash remaining on) it was changed, not an expensive bit of kit. New unit fitted, code light now flashing but still no go. This was interpreted by Alfa Distributors in Ireland as indicating a fault in the engine ECU. To ensure that code light flashing was not a fluke caused maybe by code unit being disconnected the old code unit was re-fitted. Code light now remaining on. New code unit re-fitted, code light flashing again.
Removed engine ECU and sent to a specialist in Southampton who said they "could find no evidence of any damage and the chip was running" When asked was the unit working they repeated the diagnosis. So no joy there. They did however supply pin out identification for the 50 pin plug that connects to the ECU. One of these pins is 12v+ fed from the battery, one is 12v+ fed from the ignition switch and four are 12v- to the chassis. I tested all of these and they were in order. The only answer was to replace the ECU, approximately Euro 850 (GBP 550). New unit fitted started first time. Key code light was flashing but engine was running!!
Switched off, inserted master key, turned to first position, code light came on, removed master key, inserted both standard keys, turned until code light came on, removed, inserted master key again, turned until code light came on, removed key, now both standard keys work properly.
From reading between the lines and getting feedback from many people in the trade who have had related problems, I believe that it started with jump starting the car from another car which had its engine running. I discovered a warning in the owners manual which says "never to use an auxiliary power source to jump start the engine, only use a battery" Does an alternator on another car possibly qualify as an auxiliary power source. I know that if a battery is disconnected when an engine with an alternator (most modern cars) is running, there is no back EMF to control the voltage and the alternator can achieve very high voltage levels for a couple of seconds. This would blow most electronic equipment.
Alfas, son't you just love them!!!