colorado silver

Today I was test driving a 97 A-4, 1.8 with Greddy boost, triflow, Blitz blow valve and the car ran great. However at low speeds like 35 mph in second gear if the car was under steady throtle it would from time to time have a bobble or miss. the owner said it had done that for a long time and all he did was either shift or add throttle and it would go away which it did. no signs of this under more agressive driving or in higher gears(at least while I drove it) It sounds like a waste gate or maybe the blow valve but I do not have any experience with these cars. other than that it runs perfect. any help or Ideas would be helpful
Thanks