Heater Temp. Control Valve

[FatButtFast]

The temperature valve (98 Griff) motor does not seam to be operating correctly. Sometimes its fine with the motor operating the valve from fully open to closed, and at other times it just sits there oscillating half a turn forwards and backwards (operating the rotary switch has no effect). When its is oscillating it does so continuously from ignition on.

I have had a look at the unit under the glove compartment, and can not see any limit switches that may need adjusting. The motor and valve also do not seem to be fixed to anything either (just suspended from the pipe).

I would be grateful for any ideas.