ok, just getting back with a bit of info, mite be a bit of light at the end of the tunnel. im not on for naming and shaming the guy who fitted the belts as some people decide to go on the witch hunt when they get that info. but i decided to get my hands dirty today and got lend of the equipment to carry out a compression test.
results as follws.
cylinder 1 - 175psi
cylinder 2 - 190 psi
cylinder 3 - 190 psi
cylinder 4 - 160 psi.
so possibly head gasket causing this, i also noticed a slight oil leak at back of engine near the flywheel side.
got new cam shaft end caps coming tomorrow so gona get the timing checked and have a new lambda sensor coming also so get that problem sorted and see where we go from there.