Working on a GM / Buick 3800 V6 Series III in a 2005 Buick Lacrosse that wouldn't start and run The car ran fine when it was parked, but wouldn't run after an overnight soak at about 10 Degrees F. And, it didn't improve over the next few days. I used an OBD2 scan tool to diagnose the engine and find that the MAP sensor was suspect. Disconnecting the sensor temporarily confirmed that the sensor was likely bad. Actually there are many times where disconnecting a sensor will improve a problem. If OBD2 hasn't yet tested the sensor as bad, if you disconnect it, the computer will use a backup value in many cases.
A new MAP sensor was installed and the engine now runs great. I'll show the data that I recorded and how I decided the MAP sensor was bad.

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