Low idle and a whine

[Alfashark]

Brought the Coupe up to the top of the drive for a quick pre-warrant once over, all was well - running and idling smoothly. Brushed against the oil pressure gauge wires and all of a sudden, its down to a 400rpm idle
Still revs sweetly, and seems to have normal throttle response but it just returns to a 400rpm idle, and a very smooth 400rpm at that.

Checked out the tailpipe and it has a smooth note, and isn't blowing carbon or any smoke or steam... has got me buggered, neither Fabian (our flatmate) or myself touched any part of the engine apart from that sender wire...

Also, the engine has always had a whine that rises and falls with throttle input... We've pulled the front over off and used screwdrivers and stethoscopes on it, but have never been able to find the source.
Today this has gotten louder (as in blown small-block), we've just pulled the front cover off the engine and used the screwdriver stethoscope trick, and we are both pretty sure it's not the cambelt tensioner, nor the p/s pump... possibly the water pump or oil pump drive (I'm assuming the oil pump drive is at the front of a 5-pot?)

Any ideas as to where to start hunting or diagnosing this further?

[Alfashark]

UPDATE: Idle now sorted
Top radiator hose housing on the block has a 2-wire plug for a sender on the top side, and a small metal nipple underneath the housing (hidden by the hose itself) this is supposed to have some kind of connector for a sensor plugged onto it - mine had a scungy female spade connector hooked up to it... fitted like a hotdog thrown down a hallway, so we must have knocked this and broken what was left of the connection - put a shiny new spade connector on the wire and have secured it until a more permanant connection is hooked up, and the car idles just fine now

Interestingly the whine got much quieter after reconnecting this wire

[kerker21]

do you have an earth wire from engine to body there should be two one front from rocher bolt to slam pannel and one at rear as if not it could be earthing through wiering loom and you dont want that nonono , duz the wine stop when you loosen the oil filler cap to let air in to the head , as it could be the rear crank oil seal wineing as thay start lo pass oil and it glazes the crank end and acts like rubbibg your finger around the rim of a glass effect my wr did it and it drove me mental trying to find out what it was , start her up let wine start then undoo oil filler cap .

john...