help with coolant temp sensor?

["Creel, Kenneth E" <Kenneth.E.Creel@den.mmc.com>]

I'm getting a fault code on my '90 90q20V (99k miles) that says that 
the coolant temp sensor is bad.  I looked through the Bentley and I'm 
a bit confused as to the location of this sensor.  One diagram points 
me to a location between the engine and firewall, another to a point 
the lower part of the engine where the coolant hose enters (beneath 
the fuel injectors).
a)where is this part?
b)is this the same sensor that feeds the dash gauge and the climate 
control (on diagnostic channel 6) ?
c)the temp gauge appears to behave as if only the thermostat is bad, i.
e., normal temps in the city, cool at high speeds - so my inclination 
is just to replace the thermostat.
d)could this have anything to do with my cold-starting problems?

Thanks,
Ken Creel