I do recall that when he had the sniffer on the passenger side (the good side) it spiked up briefly to 18 and then back down to stoich. Then we moved it to the driver's side and it stayed at 17ish. My guess is that perhaps the problem WAS across both sides but was intermittent, so it just appeared that only one side was at 17.
"Find out just what any people will quietly submit to and you have the exact measure of the injustice and wrong which will be imposed on them." - Frederick Douglas