Hey what up?? i have a 94 z28 lt1 and when im driving around my speedometer goes up to my speed then it drops down and it start running really rough. and like the maximum speed i can go is like 90 with the rpms at 6000 also i noiticed that if im going like 40 mph and my speedometer reads like 15 it wont let me put cruise control on, even tho im going faster than 25. But it lets me put cruise control on when the speedometer says im going faster than 25?? So i think this is somekinda sensor? What do you think it is?

 

sounds like the Vehicle Speed Sensor on the tranny

could cause the car to go into limp mode if it takes a dump and lock out gears

 

How about the vehicle speed sensor (VSS) on the tranny tailshaft housing?

Are any other gauges acting up?

 

nope its just the speedometer gauge, also when it runs rough i can hear this very loud vibrate almost like a grinding noise coming from the bottom of the car?

 

Check the VSS and the output shaft of the tranny. Do you have an A4 or an M6?

Why not add a "signature" with basic info about your car?

 

Alright its an automatic, what am i looking for on the speed sensor? what happens if i take it out?

 

The sensor is a magnetic pickup, pushed into a hole in the tailshaft housing of the tranny. The output shaft has a reluctor wheel on it, and it rotates right next to the sensor. Sounds like the wheel may be hitting the sensor. Pull out the sensor and look for damage.