Why does my 97 Tiburon FX surge at highway speed. on 1997 Hyundai Tiburon

Its been doing it right after I bought. So about a couple of days now. Only does it when easing on and off the gas. If you hit the gas hard it doesn't do it. Changed plugs, wires,cleaned idle air control. What else could it be? SOS

2 answers
CHECK ENG. LIGHT ON? SOUNDS LIKE THROTTLE POSITION SENSOR. GET IT SCANNED BY A SHOP OTHER THAN AUTO PARTS STORE.
seek diag and est from a good mech