help with coolant temp sensor

94 chevy 3.1 lumina euro.. replaced sensor and no temp reading but gauge jumps when car is started I was hoping for any suggestions thankyou.

Sure you replaced the right one? There are two. One for the ECM, one for the gauge.

I think that I replaced the one to the ecm its is by the thermostat where is the other one located?

The one for the guage is in the rear cylinder head, between cylinders 3 and 5, with an 8" single green wire coming out of it.