the waxstat is a very primative unreliable fast idle mechanism.
when the coolants cold, the wax shrinks and the plunger is resting low. this allows the sprung loaded fast idle arm to push against the throttle mechanism and keeping it slightly open, hence "fast idles" at 1400rpm during cold starts
once the engine & coolant is at 82C, the wax expands to move the plunger up against the sprung fast idle arm. this retracts the fast idle arm away from the throttle mechanism and allows the throttle to fully shut therefore warm idles at 750rpm.
over the years of heat cycle, the wax tends to stiffen up so it doesn't expand as much or at all even when the engine is fully warm, so the mechanism remains stuck in "fast idle" mode.
so the first symptom of a seized waxstat from date of manufacture is remaining stuck in fast idle when engines warmed up.
I say "from date of manufacture" cos when it seizes, most ppl take it to a garage and would mostly just tighten the "idle bleed valve" to lower the warm idle speed as a bandage, even though the throttle is still propped open by the fast idle mechanism.
another thing is the IACV at the front of the TB is an electronic backup of the mechanical fast idle mechanism.
the solution is to disable & discard the old waxstat mechanism from the throttle, clean and check the IACV so its functioning 100% and then readjust the idle bleed screw till it warm idles at 750rpm.
i've written a remedy guide here:
http://micra.org.uk/threads/pollymobiles-rebuild.35251/page-19#post-446256
