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Have problem with map sensor reading,while checking wiring I have a 5 volt feed 2.9 volt sensor but on the ground I have negative0.1 volts why is it a negative reading any ideas thanks.
That means you are measuring 0,1 volts of potential between your leads, and if you switch your wires on your meter around it will show positive. It could also be some kind of galvanic voltage you are reading if there are different kinds of metal, gold for example.
Where do you have your ground lead when measuring?
Probably just noise, especially if you checked it with the engine running. Ground voltages can vary depending on where you measure between, for example measure the difference between battery negative post and the block with the engine running.
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