Loads of cranking and smoke then starting sounds like it was flooded.
Car is more likely to flood if spark plugs are fouled (Not changed for a while, only used for short journeys or not revved often enough)
Does the car turn over ok everytime? On Micras when you turn the key the fuel pump relay actuates but if you turn it off and straight back on the relay wont work. You have to give it 10 seconds or so between starting attempts. If the starter switch is on its way out you could be interrupting the starting without knowing.
What temp sensor did he disconnect? Surely a dodgy sensor would bring up a fault code? I know Vauxhall ones used to go faulty and not bring a code up but the only temp sensors I've ever had to change were the ones that control the temp gauge (which is a seperate sensor) I think this was the reasoning behind the AA guys actions.
Does your car have the red chip on the key. 2000 is the year they changed, isnt it? I was under the impression (from Ed) that his immobiliserless ecus will only work with pre coil pack cars (ones with the red chip, not blue chip)
I would try a new set of spark plugs before anything else. I would only change the temp sensor if it showed up as incorrect on the data list or brought up a fault code.
