I recently purchased a Bontrager Turbocharger floor pump. Seemed to be pretty good. However, I tried to check my tire pressure Friday night before my Saturday AM ride, and I have no idea what pressure I inflated my tires to. Once I started pumping, the guage had a mind of its own. While I was pushing the handle down, it would spike to between 120 and 160 only to quickly return to a much lower number. I jumped pumped them up 'til they were firm and hoped they would be OK. Does it sound like I bought a lemon?