Senor is located on the pipe at the back of the engine block on the 1.9, nowhere near the viscous fan. Get an OE one, green, with 4 pins. A simple swap but you will need to top up the coolant after.
This was happening on my 1.8t cleaned the connector to the top of the sensor and no more erratic needle it's as though it was a dirty connection might not be on yours but worth a shot