Distributor, Crank Position Sensor and Idle Control Valve are connected to this part of the loom, this remaining plug is spare. I've borrowed a picture to show all the plugs.

http://i182.photobucket.com/albums/x...=1508180219133

It appears to be a cable much larger than standard 1.5mm coloured wires with a copper outer.

Can you help identify the plug please?

 

Could be the sensor (air temp) in the plenum.

It goes in the threaded hole in the middle of the plenum in this picture

 

Here's a useful site with diagrams,

http://www.bigturbo.co.uk/main6.htm

​​​​​​Get a multimeter set it on continuity and check where it goes

 

Thanks for your help guys. This was the knock sensor plug apparently, I don't have a knock sensor though. Will leave it disconnected.