2000 Ford Taurus SES p1506 code?

Got a code for p1506, manufacture control, aka iac valve, I changed the iac and it was indeed pretty dirty but did not fix the problem. I installed and cleared the code, same code popped up

Defective Idle Air Control (IAC) valve
Open or shorted IAC valve harness
Poor electrical connection in IAC valve circuit
Intake leaks
Stuck PCV valve

You should check the connector for the 5 Volt Reference signal. It's critical to proper operation. Vacuum Leaks will cause it too, check all your lines and fittings and look at the Throttle Body Gasket. And PCV Valve and Grommet.