5kt fault codes

[jjwjr@ix.netcom.com (JEREMY J. WALTERS JR.)]

I am trying to track down the cause of difficult cold starting in my 86 
5kt.  The engine will start and run smoothly, but needs to be cranked 
for a while.  When checking for fault codes in memory, 2312 is the only 
input diagnosis code to appear.This is supposed to be for the coolant 
temp sensor.  I have checked this and the blue wire to the ECU, and 
they seem O.K.  Is the 4-prong thermo switch under the coolant outlet 
also associated with this code, or am I missing something?  The ECU is 
a MAC 11B by Hitachi. Do I also need to display the output fault codes? 
(with engine off)  I am baffled!