95lhs Problem Ergggggh.

My 1995 Has Developed A Problem After My Mechanic Installed A New Fuel Injector, And Intake Manifold Gaskets. Now My 95 Lhs Surges,(the Engine), Approximately 400 Rpm When You Try To Hold The Car At A Steady Speed. It Idles Fine And Accelerates Great, But At Any Speed You Try To Hold Steady, It Surges Badly. My Mechanic Put On His Scope And Found It Was The Throttle Position Sensor, We Replaced It , No Difference. Any Body Out There That Can Help Me?