I have a 1990 240sx with a five speed. Heres my problem. When i start my car the speedo goes to 35 and the second i barely move the clutch it goes to 45 no matter how fast i go. As soon as i come to an idle it pulses down to 15.

I just had the v.s.s (vehicle speed sensor) on the tranny tested and they said it was bad so i went and spent 80 dollars and got a new one and replaced it. My speedo is still acting weird. Can any one help me please.

check the cable and or wiring, I don't know which one your tranny has.

If you have a cable hook up an electric drill to it and turn the drill on, see if the speedo moves properly, this will tell you if its a speed sensor problem, a tranny problem, or a cable/instrument problem. If it messes up still your looking into the cable or actual gauge. If you are sure the sensor is good perhaps the gear its driven off of inside the transmission is faulty.