Air leak somewhere? Inlet manifold gasket perhaps. Rubber vacuum hose split somewhere. Is one-way valve (plastic white/black thing) for venting valve cover OK? Poor connection to air-mass meter. Timing set correctly when you changed chain, did you rotate engine a few times to check sprokets and flywheel marks all lined up? Usual problem with poor idling is the AIC valve, this controls amount of air by-passing throttle plate at idle, worth cleaning it.
Can you give a more detailed description of the problem, how often, hot or cold engine, when more electrical load on the engine etc.
Many thanks Adrian for trying to help,have not tried any of your suggestions yet,engine will now tick over, but appears to judder on and off,with slight vibration as if a mounting is loose,this seems to come and go but only when ticking over, when in drive (automatic) engine sounds great, and car drives very well.
I've got exactly the same bus. Likewise - my judders sometimes (more noticeable at low revs). I reckon it's the DI cartidge failing - one of the coils breaking down. Perhaps have that off (4x 10mm bolts!) and clean them out. Other than that, it's a new one... assuming I'm right.