I have a 91 TA, 305 tpi, 5 speed. When my car is in 5th gear and I give it gas the speedo drops to zero, but When I let off of the gas the speedo goes back to normal, and reads the correct speed. My car only does this in 5th gear, which is weird. It started doing this yesterday. All of the other gauges work perfectly, except for the speedo. I don't know what's wrong, any input is greatly appreciated !!!

 

Did youupgrade anything electrical? My brother owns a 91 WS6 and he bought all MSD ignition ( control box, coil, wires) and has a powerful sound system. His Tach would be fine until he punched it, the the tach would go to zero, then jump back to regular when he let off it. We think its maybe his alternator, or the wires in his car cant handle all the load. Im not sure if this could happen to your car, but its a good shot. Also, have you checked your VSS? Its a sesnor that plugs into your trans. Sorry if I just made you feel like a little kid, im not sure how much you know, after all, we have never meet . Also, you can try looking for any shorts in the system, or, check the sensor to see if the pickup in the sensor is bad. Just listing off what comes to mind. Let me know if any of this works, hope it does, good luck.