I am not really tight with the D22 instrument cluster, but I'd assume one of three possibilities:
1) The bulb in the dash is slightly dodgy. I've had bulbs break their filament and work intermittently and it was only when I was turning the bulb over in my hand that I noticed the filament fall away from the connection.
2) The instrument cluster has a poor earth (this IS a D40 issue). Not sure if it will be your problem, but check to see if any OTHER globes or instruments are not working normally - if everything else is ok, it won't be the earth. If something else is playing up, you might need an auto electrician. In the D40, the solution (believe it or not) was to add an earth wire from the stereo to the bodywork under the dash.
3) Faulty airbag diagnostic module. This happened to me. I had to replace the module - Nissan wanted over $1K (Australian dollars) and a wrecking yard sold me one for $100 - I figured that a car wouldn't be wrecked because the airbag module was faulty and it worked fine. T50 security torx bit was required to remove the module in my D40, the D22 might be the same.
