The none turbo cvh's always tend to tick over a bit more lumpy compaired to the turbos. My 3i had a really bad miss fire at tick and I have replaced everything I can but still won't over smooth. I have learnt to live with it but if it is really bad start with a service, if that does not sort it check the leads. Get the mixture adjusted, any garage that does mot's can do it for about £20. If it still does it the look at the MAP sensor, idle control valve, crank sensor, find out the last time the belt was changed as the timing could be out slightly, the fuel pressur regulator may need adjusting and a decent garage should be able to do that. Another possible is the fuel pump, mine was running really rough just before the pump died.