Thanks for the reply, I've been tearing my hair out over this.
Firstly, there's no pattern to it.
It first started a few weeks ago after the car had been parked for 20-30mins.
It wouldn't start, sounded like it was out of fuel. I thought it was the immobiliser, got out of the car locked it unlocked, nothing, worried about flattening the battery I waited a few mins.. randomly pressed key buttons, it started first time.
Initially thought it was the key as I could hear the chip had come loose, so I switched to the spare key and no problems until a few days ago when I was pulling up to stop at the tail of a traffic jam (Highway, rh lane of course) and it just conked out and wouldn't restart, so now I know it wasn't the key because that key is miles away. I tried pushing buttons and waiting etc, but this time I flattened the battery. Help soon arrived and all I need was their jump pack and it started and I was away.
I got home and poured over the owners manual and found the emergency start procedure. I had the code in my wallet all the time, haven't looked at it since I put it in there 4yrs ago, and my ignorance doesn't help.
Then I trawled the web and this site for any clues.
Armed with my new info I went for a drive and tried to re-create circumstances, rolling to a stop etc. Nothing.
A couple of days ago it did it again as I was crawling to a stop in 1st. With plenty of room in a safe area I started to follow the emergency start..turn key to MAR depress accelerator and wait for engine light to flash etc.
Anyway, no lights appeared on the dash,but after just holding the acc pedal for a while,it started.
That's when I took it to Alfa.
They say they scanned it and can't find anything, but say the battery is holding too much charge(whatever that means) they want to replace it and scan again and saying it MAY be the ecu.
I don't understand why I have to buy a $200 battery, I would have assumed they used a test battery.
Sorry this is so long, but in answer to your question.
"When you say the car "triggers the immobiliser" - do you mean that the key symboil is illuminated, preventing the car from starting - or just that the car cuts out - but will restart after a while?"
I'm guessing immobilser.. No warning lights or symbols and it always restarts.
It's a long weekend here and the car is locked away until Tues. I don't know whether to cut my losses and get the car back, give them $300 for nothing or grit my teeth.
I feel totally snookered