I am just used to it but thought I'd try and fix my idle.
I wonder if any one has tackled this problem? I have owned 2 84's and an 85 and all have done this to a degree.

My car idles perfect at 750 until I brake. She drops just a little but still like glass. However, when the lights go on, I get a good 150 rpm drop and rough dle. Also, the interior fan drops the idle significantly as well. However, no matter how many things I turn on, she won't die down below 600 rpm, just idles rough.

I am pretty sure it has to do with a comination of vacuum and alternator. My alternator charges fine, but I think those are only 65 watt alt's in the 7's.

Has anyone had this problem and tried a different brand alt or maybe found out it was old coils or something? I am thinking that the aging alt at the low rpm's plus those power hungry coils are starving my plugs.

Just wondering.

 

It sounds like the alternator. If it's original, it's probably time to replace it.

One thing you can do before you get a new one is to adjust the idle to come up to 1k and drive it a while and see if the problem still occurs.

 

An electrical load is the same thing as a mechanical load when it comes to an alternator. Lets say your alternator is producing full power at 65 Watts. Now lets say that the alternator is about 85% effecient at converting mechanical energy to electrical energy. That's about 0.1 hp robbed right there. Not much, but at a 750 rpm idle, the motor isn't putting out much hp to begin with. An alternator going bad will not be able to meet the demand of the electrical system, and then you start drawing off the battery. Weak spark could contribute to lowering the idle more I suppose.

 

That's what I am thinking, low power from the alt at low RPM's. My question is, what are there for upgrades to the 65 watt job that the car came with? I would like to go with a 85 watt or higher but have no idea as to bolt compatibility.

 

If your idle drops when you press the brake it means your idle mixture is set too lean. Try richening up just a little to compensate for the extra air being drawn in when the brakes are applied.

 

I will try your advice with the mixture. I am going to have a O2 Sensor installed so I can actually figure out whats going on now.

Oh, I did some checking on Autozones parts site. A 86 to 88 is 70 watts. 89 and higher are 80 watts. My 85 is 50 to 60 depending upon make. Can anyone who has a 2nd gen tell me if the spacing between the flanges on the alt is the same as their 1st gen. I would be inclined to believe so. For only about another 30 bucks, it would be worth it to get a 80 watt vs the 60 watt.

 

I have a 2nd gen alt. in mine. It does require a different spacer but that's no big deal. I just used an appropriate sized nut.

With the idle mixture, just turn the mixture screw maybe 1/4 turn anti-clockwise and it should do the trick.