2000 Vauxhall Corsa Coolant temperature sensor in need of r

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 the cause of a hesitation issue with my girlfriend's Corsa.

During accelaration, at some point approx between 2 and 3k rpm, the car loses power and the revs stop rising. After maybe half a second, the power returns and the car accelarates normally again. All well and good unless you're trying to get out of a junction - not good. No engine management lights appear when this happens. The issue seems to be more noticable when the car is warm for example when coming off the motorway and then stopping at a junction and setting off again.

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

The next (and last) thing on my list 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 you can shed some light on this for me

Many thanks and kind regards

Dan