1) Make sure that the engine is warm, but not hot.
2) Turn off all electrical items (fan, radio and lights)
3) Start the car and after it settles into a regular idle notice where the needle is on the tachometer. It should be just over the graduation mark below the "1". (around 850/900 rpm)
4) Bridge the TEN and GND cells
5) You should notice the idle speed change after a few seconds.
6) Have a look at the tachometer. If the ambient idle speed moved then you have discovered the problem.
7) Slowly turn the idle screw until the revs come up to just over the graduation mark on the tachometer.
8) Do this slowly, as there is a slight lag in screwing and response.
9) If the radiator fans come on during the process then stop adjusting and wait for it to go off.
10) When you have it idling where you think it should be remove the bridging wire. In a few seconds the ECU idle setting will kick in. If the engine remains at the same rpm then you have matched the ambient idle to the ECU setting.
11) If not, then replace the bridge and adjust the idle screw,
12) Repeat steps 10 and 11 until the idle speeds are matched.