240SX help

[ashley240sx]

I have a 90 240Sx and i am needing some help with it. The speedometer is not working and we have tried different things such as a fuse and we seem to not be able to get it working. does anyone know where or what it could be that its not working? also, when i start the car and its in park it idles fine but as soon as i put it in drive or reverse it idles rough. Does anyone know why it would be doing this? if you could help me out that would be great. thank you.