Help? E36 328i air leak under intake manifold and limiting at 5000rpm

[james328i]

Wondering if anyone can help. As above
really. This problem has developed over the last week or two. It started off with an air leak underneath the intake manifold. I can hear it but can't quite see where it's coming from. How easy is it to remove the intake? I have a split heater hose that needs replacing which is also underneath the intake manifold. I can hopefully do it all at the same time. Would the limiting at 5000rpm be linked to the air leak? I have read somewhere that I could be camshaft/crankshaft sensor, how can I tell if this is the possible cause?

Cheers