I have a 91 crx si with a first gen b16. turbo. and heres my problem.

Ok soo latley i noticed that my temp gauge in the cluster seems to rise really fast ans then dip, and basicly after that its like up and down like wave motion. I dont think my fan is coming on that often eaither, or not staying on long enough, sh#t gets way to hot.

 

sounds like a loose ground, bad connection. Check if the fan turns on by shorting out the fat switch at the thermostat.