Mick,
The reason I asked about the heater was that, if the thermostat is permanently stuck open, the coolant will generally be on the cool side and therefore the heater runs cooler. I know the Elan heater is not the best there has ever been, but if your coolant is only 60°C rather than 85°C, the heater will be piss poor.
I reckon if you change the thermostat, you'll cure the variable tickover AND improve your heater.
Geoff

