It seems from going over all the relevant threads, that a significant number of people running JDM engines in the US experience a bad hesitation/stumbling/misfiring/low power problem at lower RPMs (1000-4000rpms). People have gone crazy going through great efforts to solve this problem with little sucess, including replacing or cleaning components in all the following categories: IGNITION spark plugs, wires, distributor, distributor cap & rotor AIR PCV valve, EGR valve, EGR intake ports, throttle body FUEL fuel filter, fuel pressure regulator, fuel injectors SENSORS knock sensor, MAP sensor, TPS sensor Whenever someone seems to solve the hesitation problems, it is temporary or an inconsistent fix. Not all cars with the hesitation are probably having the same problem, yet the high frequency of JDM engines with hesitation suggests there is a common thread. The one thing that JDM engines do all have in common is higher compression, and that the engines and their ECUs were designed to run the higher octane fuel available in Japan. I'm beginning to agree that this is the most likely explanation. I think the root cause of the hesitation is the knock sensor sensing knock due to the lower octane fuels available in the US detonated in the higher compression engines. My hesitation problem is especially bad, and I am running an S Spec H22 with 11.0 compression. So if anyone has more info on this, let's make this thread useful. - If you've done a swap, state what kind: regular JDM, Type S, S spec, OBD1, OBD2, etc. - If you are having the hesitation problem, say so and describe it. - Any new definitive fixes, theories, etc. For example, if you are using octane booster has it consistently solved the problem? If you are running a P28 or P72 with P13 knock board and a Hondata, has that solved your problem? Has getting your fuel injectors balanced been a long-term solution?