2000 Vauxhall Corsa Corsa coolant temp sensor loose

Engine Performance problem
2000 Vauxhall Corsa 4 cyl Front Wheel Drive Manual 70k miles

Hi,

Over the past few months, I have been trying to track down a hesitation problem with my girlfriend's Corsa.

At some point approx between 2 and 3k rpm, as the revs are picking up, the power suddenly disappears and the revs stop climbing; after a split second the power returns and the car is fine. All well and good unless you're trying to get out of a junction - not good. No lights appear when this happens. The problem is much more noticable when the car is warm for example after coming off the motorway when you stop at lights and then set off again.

To try and track down the problem the following have been tried:
o Changed Coil pack with one from a known working car
o Changed Crank sensor (changed to fix another problem)
o Changed Air flow meter with one from a known working car.
o New Plugs and filters
o Checked and WD40'd all connections and block connectors

The next (and last) thing I am going to try before biting the bullet and spending some money by taking it in somewhere is the coolant temperature sensor. One thing I have noticed is that the middle copper core bit of this sensor, the bit that the spade connector slides onto, actually seems to spin round in the sensor body. Is this normal? I was just wondering could this be causing a loose connection. I can send a picture if need be.

Hope that makes sense

Many thanks and kind regards

Dan