Re: 1,8tspark 156 - Doesn't always start. Help please
Does the "code" warning light ever stay on? This happened to my 156, a 1.8 tspark like yours. I had to get the code from the dealership (about £30) and use that to start the car every time, though it began as an intermittent problem. The engine will turn over but will not fire if the code in the key is not recognised, but simply removing the key and starting again sometimes makes the problem go away for a bit.
Mine turned out to be a faulty ECU, cost about £200 to replace. All derived from a faulty battery a few months beforehand.