87 civic si d15a3 is missing when i drive on the freeway at 3500-4200 rpm(70-80mph) ive tried changing spark plugs,ignition wires,rotor cap, button and i use 93 octane gas??? i dont have access to tools for checking the timing but i hope its a simple sensor.it runs fine at any other speed and doesnt have anykind of rythm to the miss.any thoughts?