My 1997 Infiniti J30 is sometimes very slow to get any power when I start going from a full stop. I can put the pedal to the floor, and it will slowly creep forward for 3-5 seconds, then suddenly gets enough power and picks up speed. It only does this sometimes. On some days, it will have perfectly fine acceleration. Other times, it will be slow like this right off the bat. In some cases, it will work fine for part of the day, then start being slow after a couple hours.
Previously, it's engine timing was way off, and it had a bad o2 sensor. I replaced the sensor and had the engine timing fixed (w/new belt and water pump as well).
I thought it might be spark plug related but I can't figure out why it would be bad for hours on end or good for hours on end at different times. I would think a spark plug problem would be consistently bad or good.
My theory is that the ECU is still used to trying to work with the bad timing, and needs to be reset to relearn the right air/fuel ratios. (I don't know why it wouldn't be bad all the time though, so maybe it's something more than this) I can't find specific directions for how to fully reset the ECM for this make and model anywhere, including a service manual I found online. I have tried the method where you turn the diagnostic mode screw on the ECM, and the method where you take the cables off the battery and hook them to each other to drain the voltage in the system, and a couple other "This always works for all cars" methods found online. The problem doesn't go away.
Thank you in advance for any ideas or suggestions.