Bought a 1988 accord LXi Coupe and have a perculiar problem I Need help/advise on... she runs fine, smogged perfectly, but under mild to mid-range accelleration I hear a sorta popping sound and I sss the tach fluctuate 500-1500 rpm per pop.. what are some oif the most likely causes of this? The plugs, wires, cap and rotor all look new...