Idle solenoid

Is there any method of testing the idle solenoid or signal from the ECM on a
'92 Metro? My engine still drops about 150 rpm as electrical accessories are turned on. The biggest drop occurs when the headlights are turned on. The alternator keeps the battery charged, so I don't think it is a problem. The solenoid for the A/C works fine. The idle speed has dropped as low as 750 rpm and is very rough at that speed. Starting to wonder if the motor mount isolator bushings are bad the way the motor shakes at the lower rpm.
Any suggestions will be greatly appreciated.
Thanks,

There's a separate circuit that raises the idle when an electrical load is turned on, but I think it uses the same idle control system. Some cars have an Idle Air Valve and some have an Idle Control Motor. Yes, there are test procedures in the FSM.

All that being said, I think the early cars are supposed to idle at 750. Low and rough idle is usually a burned valve, compression test is in order.

so is the idle speed listed under the hood the idle speed without any headlights or accessories turned on? I've always wandered that

when i turn on my headlights my idle will drop, then go back up. is this normal?

Geoff