1985 Pontiac Trans Hi This Coolant Temp Sensor Replace Sensor Pigtail

Hi,i have this problem with the coolant temp sensor.I replace the coolant temp sensor and the pigtail,but as soon as i put the pigtail on the new cts my car run rough and start missing or shake.I replace the cts again,same thing,we check for broken wires all the way to the pcm,,found none,when i install the pigtail again on the cts,it make my car run bad again,i had the pigtail and sensor check at auto zone,its all good..Could this be my pcm going bad ? i just dont understand this.theres no open wires or split wires going from the pcm to the cts.i have been trying for 2 weeks figuring this out,cant get it.do you know whats causing this? it only run bad when i connect the harness pigtail to the cts. I hope to hear from you soon.And thanks......Glen ps..my car has the electronic rochester carb