ok i just got an 87 trans am i think the guy before me did an engine swap cause its carbed not tpi. anyway. the temp gauge shoots up all the way. the car isnt overheating. but what sensor would cause a faulty reading on the gauge or is it just the gauge thats bad?

 

what motor are u talking about, Well 87 did have carbs on its v8, but it could be the sending unit for the guage it located on the driver side between cylnder 1 and 3 on both of my 87's(on my gta with the digital dash i first thought the gauge went bad b/c its digital but it turned out the clip on the sensor fell off so it was a simple fix for me)

 

gotta be a sending unit i noticed today when i started it up the needle would jump from cold to hot extremes without cause. only thing i can think of is a faulty sending unit

 

The temperature gauge sender is in the driver side head between the front two cylinders. You could try replacing it, but I'd probably try a new gauge.