rpms drop when lights are first turned on

[88SupraTurbo]

exactly what the title says... my 88turbo usually idles at about 600-700rpms when its all warmed up and then i just noticed that when i turn on the lights while sitting at idle my rpms drop to about 500 when the lights first go up and then the rpms slowly rise back to normal. is it normal for this to happen?

 

[Milenko]

Yes, that's normal. Turning the lights on (especially with the fogs and/or high beams) puts additional load on the alternator which puts more load on the motor. The ECU then adjusts idle speed with the ISC to bring it back up to normal speed.