Isnt the temp sensor test you did giving you the clues. It is likely to be just a fuel mixture adjustment that is off. If it were the air sensor pot, it would not have worked well when you attached the resistor. And if the coolant temp sensor resistance changes properly with engine temp, and is close to 2.5-3.5K at 20 deg-C, then just enrichen the mixture a bit and most likely you would be fine.

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Saumil S. Patel