Sensex fell by 166 points at 17164 in the noon trade today. It opened over 92 points down after rising the most in nearly 10 months in the previous session. The 30-share index had surged 561 points in yesterday.The National Stock Exchange's Nifty fell 42 points to 5,151 points.Brokers said besides emergence of profit-booking by foreign funds and retail investors, weak trend on other Asian bourses was also responsible for the fall.