First, you should measure current flow to the idle control valve not voltage. The valve is a solenoid responding to current, not a switch for example responding to voltage. You go inline with the circuit (inline with one lead)in amp mode on your meter, not across the two leads going to the valve-- doing so can cause damage because you are shorting the circuit. You may have damaged your idle control unit if you did this persistently and you will probably hear a noise (a bad one) when shorting over the valve.

Second, correct current does not mean the valve itself is operating properly. It may be dirty or malfunctioning.