Though I should do an update - I took the Throttle valve assembly out and gave it a good clean (it is pretty close to the oil vent line and does get pretty oily in there). Also did some searching and the most common failure is wiring failure (insulation cracking and shorting out wires).

Having re-wired a bunch of stuff on this car (wing mirrors, phone, immobilizer etc..) I thought I'd check how hard this would be - Unfortunately it is a sealed unit (with centre pin type hex bolts) and the wiring is to molded plugs, so would be a tricky project.

However, since putting it all back together and the garage re-setting it, it is working perfectly (maybe I disturbed the wires in the right way), so I'm holding off on the repair to give me time to source a cheaper part. First sign of trouble and it goes in for replacement.

Thanks all.