Check your vacuum lines for leaks, the low miles and lack of humidity will cause cracks.
Have you checked the EGR? The port to the intake manifold clogs easily when not driven a lot.
Driving 100 miles in a week doesn't do much, unless it really gets the engine oil HOT.
I would replace the plugs (copper core) or clean and gap the current plugs. Then get the engine hot. Drive to the testing station, do not turn the engine off, and let them test it again.
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Keeping it running is better than buying new
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