Ok. A lot of different symptoms fall under "hard to start", but based on your mechanic's findings, the crankshaft position sensor could be one of the potential causes. They can be intermittent, and often fail when they become hot from engine heat.
The Engine Computer will detect the loss of signal from the crankshaft position sensor and set a diagnostic fault code in its memory. That is most likely how your mechanic was able to identify the problem even if the engine was running at the time.
Now the question is, ... Is there is different, second problem or is the problem related to the new sensor? If the hard starting acts exactly like before, the new sensor is most likely working, and there is a different problem. If the problem is worse / different than before, look more closely at the new sensor.
The air gap is critical for this sensor. The new one had either a small plastic rib molded on the end, or a paper spacer stuck on the end. The paper spacer will slide off the first time the engine starts. Its job is done. The plastic rib will wear off when the engine is started. To reuse it, the remaining part of the rib must be sliced off, then a paper spacer applied before it is reinstalled.
To check the operation of the sensor, use a cheap digital voltmeter to measure the voltage on the three wires. One must have either 5.0 or 8.0 volts when the ignition switch is turned to "run". The ground wire will have around 0.2 volts. The signal wire should vary from near 0 volts to around 5 volts as the engine is turned. If it appears to be working properly, look at the timing belt to be sure it hasn't jumped a tooth. One tooth off can make the engine difficult to start and have poor performance.
Monday, March 15th, 2010 AT 11:14 PM