So finally[I hope!]checked for air leaks found none,checked vac pipes were all in right positions[they were]cleaned icv,bought a new one[made no difference]got codes read and got a 19 cps incorrect revs or some such.Finally got round to unplugging cps to find what shape plug[oval in my case]ordered a new one from Vauxhall Parts Wharehouse in Suffolk while battery was charging[it'd gone flat due to car not being used]refitted battery and tried it ran like a good 'un,so either a poor connection on cps plug or similar!then new cps arrived in post!!so I now have a new icv and a new cps just in case,you can never have too many spares!Just need a new windscreen and I can take it for m.o.t.So thanks to all who posted their thoughts/ideas you were a great help and a source of great inspiration to keep me persevering and I can't thank you enough for that.