92 Prelude

A friend of mine has a 92 prelude with the H23A motor. In any gear if he is under 2500 rpm's it stutters a lot and doesnt have full power. He replaced the spark plugs on it and it helped a lot, but it still is noticable. What else could cause it? He has had this car in the shop quite a bit over the last 6 months for a lot of other things, but this occured shortly after he got it back this last time. I am guessing a tune up for the most part, but anything else?

sounds like it may be a fuel injector or air/fuel mixture issue. but with the information you gave its impossible to say for sure.