Heat and charging

Maybe because when it's hot outside the fan is running on high speed most of the time. When my high speed comes on I can see a descent drop in voltage. Usually when I'm at traffic lights. When I go to take off it goes back up.

Do you have underdrive pullies by chance?

Gary, if it is fan related (you only have the issue when the cooling fan [and often HVAC fan] are on), it's not uncommon from what I have seen. I have a similar issue on my 94. The car idles a bit lower with the additional load of the AC compressor and relatively large electrical draw of the fan(s), esp at night. We cant see the exact issue you're having - you might be rolling your eyes at me. I'm just not seeing what you do.

One thing to double check is the IAC - make sure it's clean and functioning (it helps compensate for the load of AC).

Otherwise I would simply band-aid by running the idle up a hair (I choose to use the throttle stop, while some prefer to use the air-bleed on the IAC).

These cars saw extensive high-desert testing but they are all now 12 years old or so and have some miles - they like to bicker at us a little bit.

Oh, Brian is sending me a controller - I'm eager to see how it helps the system-load compared to the big 'all or nothing' draw with our stock relay-driven fan speeds.

My two cents. Good luck.

It's not the heat on the alt. It's the heat that's causing the fan to opperate, thereby lowering your volts. If you are unsure about your alternator, then have it tested, this will tell you what's going on.