Car runs poorly when hot.

My daughter bought a 1995 VW Jetta from a private party. The car ran fine during the test drive. Everything looked fine under the hood. Come to find out that once the car gets up to operating temperature it starts to lose power and jerk. At the same time the check engine light flickers on and off. She has been told that it may be the throttle position sensor but I’m not convinced. The sensor is not really exposed to too much heat sitting on the air intake snorkel. What should I be looking at?