Using a multimeter, you can check the resistance at the ECT sensor, the resistance will increase (numbers get smaller as the temp increases):

68F = 2800 Ohms
104F = 1200 Ohms
212F = 150 Ohms

So a cold engine should be around 2800 and a hot engine around 150.

Many on this board suggest swapping out the thermostat and the sensor at the same time, due to need to drain about a quart of antifreeze to do either. I disagree. When the ECT fails, it is easy enough to replace without a lot of spillage - just use a finger to plug the hole. The ECT and thermostat NEED to be OEM, do not get knockoffs.

Running on a 'cold' engine for long periods due to an open thermostat will increase the likelyhood that the plugs are fouled. The ECT reading low will cause the engine to run rich eventhough the cylinder themperature is hot. Replaceing the thermostat should solve your hard start problem.

Klaus
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Always willing to listen, just not able to take direction.