Both these sensors can cause hard starting. The difference is if it happens when it is hot or cold.
If it only happens when it is cold, then it is most likely the temp sensor, not telling the ECU to richen the mixture for the start. Once it is hot it will start every time.
If it happens, regardless of the temp, hot or cold, then it can be the crank sensor. This is a magnetic pick up, that depends on the rotational speed of the crank to supply a good signal. If the sensor is going bad, it's output will be lower than it should be, at cranking speed. May be too low to give a clean signal. Once the engine starts the crank speed increases and the signal comes up the normal.
Harvey.
