As above mate, unless it's something simple (or you're lucky), best off taking it somewhere to get it checked properly. I had similar but not as erratic as your issues, when I took it to Tony @ Turbosytems he found all sorts of minor problems that caused it to run dodgy, leaky injector o'rings, leaking inlet manifold gasket, leaking exhaust downpipe, incorrectly set TPS, etc, etc... I guess for the price of a regulator it's worth changing first though.