Thanks for the replies...
Throttle switch wiring - couldn't believe I missed that diagram at the end... According to the diagram, the wires into the connector are blue/red and brown/white - which is the colour mine are before the splice (i.e. the wires going into the engine loom are the correct colours - it looks like a new plug has been chopped and spliced in at some point with different coloured wires). I may take a look at the splice to see if there are any problems there, but the fact that removing the plug makes the revs surge a little suggests that it is working. I've given the intake a clean out but the engine is breathing a little on the heavy side so it gets dirty quickly. The blue temp sender is the one that was in there, but it seems to advance okay when plugged in.
Vac pipes - already changed these today, including the pipe to the airbox, the pipe to the FPR, the pipe to the inlet manifold, both blanking pipes off the inlet manifold and the braided bit of the pipe to the clocks. The pipes I took off looked worse for wear, but swapping them made zero difference unfortunately.
Squeezing the ISV tube - will try this tomorrow. I'm also going to give the intake boot a massage to see if it changes the revs.
Throttle stop screw - don't want to mess with this if possible as it's supposed to be non-adjustable I think?
I'm still convinced there's a leak around the throttle body somewhere, given all of the oily residue under the tb.
