test for current not voltage, solenoids operate on changes in current not voltage. Put the multimeter in current mode and put the multimeter in series with the solenoid (put one lead on one end of a wire going into the valve and another on the valve lead). with that said, you probably are not getting the right current to the solenoid which leads you to the temperature sensor, idle computer or I think but am not sure, the warmup regulator. Be careful making voltage measurements at the solenoid, I once accidentally did it and it shorted the solenoid and I think it can damage the idle computer. Mine was not damaged but the sound made wasnt good. Again, measure in series for current not voltage to avoid that.