Checking the TPS on 1990 suburban

I am new to the forum and I have checked the archives for information on how to check the TPS on a 1990 Suburban. The trouble codes output on this car show that the tps is not getting the proper voltage. The sensor is new. We have checked the sensor and it is good. We have checked the wires and the voltage at the wires. I get a 5. reading with my meter set on Vdc and 200m. The reason we are checking this stuff is because the idle goes up and down when you first crank the car and it does it for about 5 minutes.