Was not aware the O2 sensor had a ground, it is mounted to the exhaust, do you have a heated sensor? In any event O2 sensor not in the loop until warmed up. Does not affect starting at all.


Coolant sensor has high resistance when cold and drops as engine warms, will not prevent starting if it has high resistance or even if disconnected.

Any other symptoms or history of how problem started?

You need 4 things to start
Starter motor turning over engine at healthy speed.
Spark properly timed.
Fuel pressure at the rail and operation of injectors.
Compression which relies on proper valve operation from the timing belt and cam.

Has anything been done to affect these things?

Have you checked radio supression relay? It provides ground to the injectors and can kill your theengine if bad.
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David Hunter