POLARITY DOES MATTER.

On 4x4 and retro fitted idle valves, they have a voltage protection diode
within the valve and if you wire it backwards it will NOT work.
(If wrong, it will effectivly short out and eventually damage the ECU)
Some valves do have a + mark on them but not all.

If it does not work, try reversing the polarity but only make a short duration
test time to prevent ECU damage !