i had a similar problem. my car would not rev under 2500rpm. checked the throttle cable and it was hella tight. maybe yours is hella loose, not opening the throttle body all the way. might not be the solution but i'd check it out.
A forum community dedicated to Nissan 240SX owners and enthusiasts. Come join the discussion about performance, builds, engine swaps, turbos, modifications, classifieds, troubleshooting, maintenance, and more!