car is a 97 ek coupe, 100% stock, automatic transmission. after driving for about 5 minutes, when the car reaches operating temperature, the speedo starts to bounce, then it will just drop and stay at zero. however, when i then take a turn, the speedo will work again, but when start to go straight, it will just drop back to zero. if i turn the car off for awhile and let it sit, it will work again until i reach operating temperature. any ideas before i go out and start to buy stuff?

 

vss is my first thought