If the temp sensor is in specs then the next thing are the two 'cold engine' gadgets.

1) Less Likely - Cold Start gas valve - this is the 5th injector gadget hooked by a fuel line to the fuel rail - off to the side fastened to the intake manifold near the throttle. It is wired (on a 72) with a ground on one side and the other side to a thermoswitch screwed into the block (right hand side just aft of the oil filter - back of the block near the bellhousing). From there the wiring goes to the starter circuit. This most likely ISN'T your problem as this just squirts extra fuel into the manifold while cranking with a cold engine. So once the started is off (engine running) it isn't working anyhow. But if it isn't working you'll have a hard time starting a cold engine and will have to resort to the 'pump the pedal' method to get it to fire.

2) More likely - Idle bypass valve - This is the aluminum gadget bolted to the head next to the thermostat (front right corner of the hear). It has two hoses connecting it to the intake manifold. Its purpose is to open when cold to allow air to bypass the throttle valve. When the engine warms it slowly closes and should be shut when warm. But they ALL get sticky sooner or later. Often they stick open and people will plug the hoses to fix the overly fast warm idle. Then it will idle far too slowly to keep running when cold. To check, pull of the hose that connects to the manifold before the throttle. With the engine cold, start it up and see if it is pulling vacuum through that hose. If not, something is amiss.

Don't be too hasty to yank the FI. D-Jet is exceedingly simple as far as electronic FI systems go and isn't too hard to keep going for a shade tree machanic (you just need the resistance specs and an ammeter) and works better than carbs. It just requires a slightly different skill set than tinkering with a couple of carbs does.

IMPORTANT TIP - when checking the resistance of various sensors (like it sounds like you did with the coolant temp sensor) first check at the sensor to see if the sensor is bad. If it looks good there also pull the plug on the ECU and check the proper connectors there as well (consult a wiring diagram). This will check the wiring as well.