Chevy Malibu surges when accelerating



I have a 2000 Chevy Malibu V6 and about four months ago it began surging when accelerating. It is an automatic transmission and manually shifting the gears fixes the problem. We’ve replaced the spark plugs, wires, coil packs, and fuel filter and fuel pump. What could be causing this problem?


Possible vacuum leak, emissions fault or perhaps an IAC valve fault.