The car pulls nicely on the lower an upper parts of the RPM band, but the middle feels weak. Might this have to do with the partial throttle closures? Also, I no longer get cylinder 6 misfire on cold start but it sounds like the motor is coughing on every cold start and I will also hear popping here and there. Might this be from the 0.018" gap on the NGK 1-step colder spark plugs or something else?