Hey Nismo Girl ... I had sort of the same problem, but it was only when I let off the gas ...
It generally means that your injectors are maxing out, or you are getting bad knock. What senors are ebing monitored on the hand controller ? I have mine set to Water Temp, Inj Duty, Knock and Revs ...
You can check the O2 sensor with the hand controller (if you have one). I can't remember off the top of my head how, but if you like, I can find out and post it up.
All sensors can be checked on the same screen, my mate has a 400hp skyline and his was having bad issues with the engine check lite, upon inspecting the sensor screen, his exhaust temp senor (in the cat) had died, unplugged it and it is all good ...
sorry if this sounds like gibberish, but I have just woken up.
Thanks ... Ian