Typically, the injectors are ground switched by the ECU to cause the injectors to operate. With the ignition switch in the run position; but, the engine not running, pull a plug out of one of the injectors and measure the voltage to ground on the two pins. For your high impedance injectors you should get 12 v on one pin and 0 volts on the other pin.
At idle, the injector operates with a relatively low pulse width. At 900 RPM it takes about 0.133 seconds to complete two engine crank revolutions (complete combustion cycle). On my B20E with sequential injection, at idle the injector is only open about 0.002 seconds during the two revolutions, so a duty cycle of about 1.5%. I assume you are trying to read the voltage across the injector terminals. Unless you have a scope or a very high end digital voltmeter with adjustable set up, you voltmeter is going to try and read the average voltage which, with a duty cycle of 1.5% would be 0.015 x 13.8 volts = .21 volts. My injectors are large resulting in relatively short pulse widths. If your injectors are OEM they are likely smaller resulting in a longer pulse width and a proportionally higher average voltage reading.