'92 Metro idle

My '92 Metro seems to drop idle speed when accessories are turned on. Mechanically, the engine seems top be sound (180# compression on all 3 cyl).Idle speed will drop about 150 RPM when the lights and heater are on, and gets somewhat rough. Idle speed is set at 950 RPM. The idle solenoid is working and activates when power is applied. Could the problem be in the alternator?
Thanks

Yes it could be. I know around here I can go to my Advanced auto and they can check them right on the car. You may want to do that if it isn't to big of an inconvenience to you.

most likely it is your alternator not generating enough power.

I believe voltage at the terminals should read around 14 volts.

I had the same problem, and needed to tighten the alternator/water pump belt.

your battery might also not be charging properly if this is the case.

get this looked at soon, or you may end up with a dead battery

There's an idle up circuit that increases the idle when anything electric is turned on. There's a diode pack under the dash that feeds a signal to the computer, then the computer ups the idle using the Idle Speed Conroller. Some cars had a separate idle controller mounted on the firewall with a vacuum line going to the throttle body, that may be for air conditioning only, not sure.