This is my first post on here and it's quite a complex one I'm afraid! I hope someone out there can help me.
I have a 2003 9-3 Aero 2.0T petrol at 108,000 miles. My car has recently developed some sort of intermittent computer malfunction. On the motorway the other day I was cruising at no more than 75mph and the check engine light came on and I lost all power. By the time the revs got to about 1200rpm the engine shut itself off. Luckily I managed to roll onto the hard shoulder and stop safely. When I tried to start the engine again it made no attempt to even try, the computer was stopping it. So I called my breakdown and he cleared the fault and said it was an O2 sensor and probably just a glitch. I carried on driving and no problems for the next 150 miles.
This morning I tried to start it from cold and although this time the battery tried to start it, it didn't. On a 2nd attempt the computer again didn't even allow the battery to try. I called my breakdown out again, he cleared the code and said it was some "internal memory malfunction" or something along those lines. He told me GM cars don't like the cold and it was probably a glitch. He advised me that if it happened again I could disconnect the battery wait a few minutes then reconnect to clear the problem.
About 30 miles later (same journey) I was travelling at about 50 mph and the same thing happened as the first time. Light came on, lost power. I tried to change gear to take a sharp left to get me off the main road but when the revs dropped the engine cut out and ended in the gateway to a field.. I was not amused. Desperate to get home I didn't bother calling my breakdown and just disconnected the battery and carried on my way. The rest of my journey (100 miles) was trouble free.
Does anyone know what on earth this could be and how I can fix it?
If I take it to a garage then the car will obviously be running, therefore no engine management light will be on, so not sure how they could possibly find the problem.
Any ideas are gratefully appreciated!
P.S I have a brand new battery, new starter motor and the MOT found no problems 3 weeks ago.
There is also a 'tapping' noise coming from the engine when it started from cold but disappears after 30 seconds.