The temp sensor for most if not all fuelies is simply a SWITCH that when reaching a certain temp tells the computer to go t the LEAN condition for normal running. Yes the switch can cause high idle.
Most likely there may be a vac leak and the computer is adjusting the fuel to make the engine run smooth and cover the lean condition.
Could also be the iac or the tps.. Not being familiar with the howell at all from here I would be simply guessing.
I would first look at a throttle stop to see if it could be advanced... if so I would atempt to retard the throttle if possible.
It could be that your pedal-cable assembly is holding the throttle open a small amount.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />