Have you checked your codes,
It could be your coolant temp sensor as it might be leaning off the fuel to much when the engine warms up and it dosnt always bring up your limp home light as the ecu is getting a reading from it ie a restance vauxhalls charge about £20,
Hope this is of help to you.
you dont have an auto choke, its injection remember
but as already stated, the ecu coolant temperature sensor does the same job on injected cars. If the sensor is shonky it will be fine from cold, then the engine heats up and the sensor is still telling the ecu that the engine is cold, then you get overfuelling. Then you have real probs starting the engine when its hot, poor running, hideous fule consumption etc etc etc.
New sensor is only a few quid anyway, change it.
sensor is the same for all engines part no. 90510183
should have no trouble getting one as they were used well into the mk3 era.