All lights dimming frequently when engine is running. Saturn SL1 1999..HELP.

I have a 1999 Saturn SL1.
My headlights and dashboard lights dim often while in IDLE.
Recently the problem has progressed while in movement. It seems that when
I shift, the dimming will also occur. When I accelerate, they light up
like normal. I also observed that when the "dimming" occurs, the air
flow(AC FAN) also weakens no matter if the A/C is on or off.
What could cuase this?
When I turn the engine off, and I'm powered by only the battery, all
lights are consistently lit. But once that car of mine's engine is
turning, the dimming begins. The idle also seems to fluctuate as well,
while sitting at stoplights.
Besides that, the car runs fine. Accelerates fine. Sounds fine. It's
just the energy fluctuating while driving that is starting to concern me.
PLEEEEEASE HELP!!

I saw on some other site that someone said they replaced a PCV VALVE
when their car "surged when starting" and "stalled at idle" . My problem
isn't identical to theirs, but in the same ballpark. CAN YOU GIVE ME SOME
ADVICE more specific to my problem?
ALL ADVICE IS GREATLY APPRECIATED.

---ROBB