Hi, my EG6 Civic (B16A) is having a weird issue. The car misfires badly under load and under 4000rpm. The idle is rough, the engine drops to about 500rpm, almost stalls, then it revs to 1000rpm and the cycle repeats. The IACV was cleaned, inspected, and the FITV was deleted, about a year ago. When revving quickly in neutral, from idle to about 3000rpm the car also misfires and hesitates. If you maintain it part throttle after 4000rpm or so, vtec engages and it goes fine to redline. No CEL codes, and the same symptoms happen with the car cold and up to temperature. The fuel pump primes fine every time and the car doesn't have any difficulty to start. Since then, I've changed the spark plug wires (VMS Racing 10.2mm), distributor coil, fuel filter and the injectors were flow tested and cleaned. The injector plugs were tested and there is pulse when running and 12v with the key in ACC. The cap and rotor were inspected and are fine. I've also ran the car with the fuel pressure regulator out of the loop and it did not make a difference. The spark plugs are NGK Iridium BKR7EIX with the stock gap and then regapped at 1.0mm to see if it made a difference, but no, same thing. The plugs were inspected before the injector job and the cylinder 3 plug was slightly wet. I've inspected them twice since then, and they seemed normal. The plug wires have been tested and the resistance is nominal. I don't think it's the fuel pump as it does not misfire at high rpms while being on the same throttle position. I'm running out of things to test and replace that are related to these symptoms. Does anyone have any advice?

 

Check the timing, both cam and spark. Also basic stuff like is it running on all four cylinders and what are the compression pressures.

All the high voltage parts of the system: coil, cap, rotor, wires, and plugs-- can pass a visual or ohm check and still have problems. Replacement is often the only way to make a positive confirmation.