Several things to consider:
1/ Don't swap out anything until it has been confirmed to be defective.

2/ You can check the Temp II sensor by substituting a fixed resistor for it.
This is best done when it is stone cold or fully hot.  Pick the resistor
value from the resistance vs. temperature graph in the Bentley.  Or, if you don't
mind pulling it, heat the sensor in some water and plot the resistance against
temperature to see if it is kosher.

3/ As Roberto said, it could be a Hall Sender queefing out.  Whenever it is
hard starting, if the tach needle is pegged to the bottom of the scale it means
that the Hall Sender is not pulsing.  During a hard start period, connect a
spark tester to one of the plug wires to see if it is sparking.  A spark tester
is cheap enough, but if you don't want to buy one, open up the gap of a spark
plug to about 100 thousandths and use it to check for the presence and
quality of the spark.  From what I have seen, about the only time to catch a failing
Hall Sender is whenever it is not pulsing the ignition and it can work one
minute and not the next.  Without the vibration and heat of the engine a failing
Hall Sender might not even show up on a distributor machine.

4/ Check the injectors.  In my experience, a failed injector can cause an
excessively rich mixture in one of two ways: either by dumping too much fuel to
burn into a cylinder or by causing the FI system to enrich the mixture because
of air being pumped through a cylinder which is NOT getting any fuel.  The air
dilutes the exhaust fooling the ECU into thinking that the mixture is running
lean and so it trys to correct the mixture by fattening it up.

George