I do have a CEL...I'm going to unplug the air pump and see what happens with this dimming light issue. I'm starting to think it's not the air pump, though.

My car generally only does this in the morning when it's cold, and then it happens intermittantly when I exit the highway and enter traffic (this is the part that makes me think it's not the air pump.) For at least a minute, the lights will dim almost as if the A/C kicked on, then bright again the next second, then dim for a second, and on and on...

I have no trouble starting the car. This condition is not affected by how many electrical loads are running (I could have both heated seats on, blower on high, wipers, rear defrost, foot on the brakes OR have nothing on at all but the DRLs.)

If an alternator will fix it, I'll slap one in there but it just seems more involved than that for some reason.

Good luck...I'm going to try to eliminate as many sources as I can and hopefully nail the problem down.