on my 97 2000, the check engine light comes on now and again. while its on, the car is way down in power (like poverty spec nissan micra power). boost is operating, oil pressure fine, water temp fine. its feels dead lumpy though, but as soon as light go's out, normal power returns. any ideas?

 

Not going into 'limp' mode is it?

 

You need to take it to be diagnosed. One or more sensors are most likely failing. It can be dangerous to your engine if left unsorted.