Temp gauge gone wacko

1999 Cav. 2.2 standard shift, Temp gauge at normal 20 min running temp. then gauge slammed to bottom like when you turn car off. did not read anything, then got erratic jumping up and down flicking between normal and cold then settled out. Turned car off, coolant good rad full bottle normal engine warm. started up again and needle went to normal then quit and jumped around got to cruise speed 60mph and needle settled to normal. Need ideas from the gang what to fix here.

1999 Cav. 2.2 standard shift, Temp gauge at normal 20 min running temp. then gauge slammed to bottom like when you turn car off. did not read anything, then got erratic jumping up and down flicking between normal and cold then settled out. Turned car off, coolant good rad full bottle normal engine warm. started up again and needle went to normal then quit and jumped around got to cruise speed 60mph and needle settled to normal. Need ideas from the gang what to fix here.

Try changin you temp guage sender unit. Or Engine Coolant Temperature 9ECT0 sensor. will be relatively cheap. Just do it with the engine cold and be ready for a little coolant to leak from the hole and wrap some plumbers tape around the thread to ensure the new one doesn't leak. This looks like a bolt with a black pug on top and on 98 and newer 2.2s is facing upwards. You should see it after looking in the engine bay for about 20 seconds.