In the past week, my headlights dim, and my blower motor slows at idle. When I accelerate, both go away. It also started to idle a bit rough at the same time the other two problems started. I'm pretty sure it's the voltage regulator. I have found conflicting information: I have heard that the voltage regulator is built in to the alternator, and I have also seen in some part stores a separate one not built in. Which is correct?

Its built into the alternator, you need a new one or a rebuilt (alternator).

+1, I agree with Turbone, your alternator is failing. Subie alternators have a built in voltage regulator. Replace the unit, and you should be good for many many more miles. It is a very ez do it yourself replacement job. Alternator sits high at the front of the motor with little around it. Remove the protective shroud, and unbolt and rebolt. 20 minute job at max.

Before you replace the alternator (it likely is at fault). Make sure the alternator belt is properly tensioned. A slipping belt will cause the alternator to drop in speed even without making noise.

Running rough at idle might be due to low idle speed.

 

Every car I have ever owned (11 total) has done exactly what you describe. Of those I only had alternator trouble on 2 of them. My Corsica, and my Cadillac. (funny they were both GM, and both gave me the most trouble). All the rest have done the same thing, not one of them ever needed an alternator while I had it. My Lincoln (which I still own) has been doing that for 25k miles.

 

I'd address the rough running issue before paying for a new alternator.

I have a Schumaker battery tester, so I tested the battery and the alternator. Both tested in the green, but just barely, being about a hair away from the edge. What I have done to try to fix it over the past 2 weeks: The plug tube seals were leaking, so I replaced them along with the valve cover gaskets, replaced plug wires (I'm now wondering if I should have replaced plugs too, but they only have 7,000 miles on them & weren't coverd with oil), cleaned IAC EGR PCV, induced Sea Foam into intake via vacuum nipple on manifold (it smoked really bad the first time, so I did a repeat application). I visually inspected vacuum lines but haven't broken out the soapy water yet. I also have not cleaned the throttle body. I am planning to do both this weekend. I hate not being able to fix problems myself, but it's starting to drive me crazy. I'm about to take it in to the shop.

How many miles are on the car?

What kind of fuel mileage are you getting?

Got a vacuum gauge?

53,000 mi on the car, mileage: ave 22 mpg combo hwy/city which is right at where it's always been, I do not have a vacuum guage, but I did check all the vacuum hoses and didn't find any leaks. I also removed the throttle body and cleaned it last weekend. Still same issues.