I'm struggling to think what pipe would need the manifold removing to fit them, they are all easy to do without removing, the inlet manifold I assume you mean, this isn't water heated, and the pipes are easy to get to from underneath, maybe the garage assumed the inlet man would be heated, most are nowadays.
This would also account for the high rpm, it is almost certainly an air leak, any air that gets in the inlet manifold without going the correct route through the iscv will cause it to idle/run faster, so it's just a case of finding where the air is getting in.
Go over the car and recheck thier work, ie that all hoses/pipes esp are fitted securely.
There is Paul Linfoot at pickering that is a RS cossie breakers, but he also works on other peoples as well, and knows what he is doing, he won't be available unfortunately for a few weeks, due to a family bereavement, but is a good port of call once settled down, he used to be in scarby as well!!
tabetha