I have a 2001 SEL and ever since I have owned it I have had the same issue. After starting and the car returns to low idle it acts like the alternator is not putting out. This is most noticeable at night with headlights on or having the the heater fan running on high. When the car idles I can hear the fan rpms drop and the headlights dim. As soon as the engines rpms come up off of idle I get a very very noticeable increase in fan rpm's and the headlights get really bright just for a second (pulse of light) then return to a steady (normal) brightness. I took it to a reputable shop and had them load test the battery and Alt. They said that the battery had a bad cell and that needed to be replaced before he test the alternator. I stuck a Yellow top Optima in and took it back to have the alt. tested. He stated the "alternator is on it's way out" he said there was virtually no output at idle and produced 88amps @ 2000rpm. Since I'm into stereos I found a 220amp HO alternator with an under drive pulley. When installing the new alternator I did the big 3 upgrade to 1/0 copper welding cable all the way around. I also ran two runs of the 1/0 wire from the front battery to the trunk and added a second matching Yellow top Optima. I figured this would finally fix my issue but I am still having the same exact symptoms. I also decided to add a stinger volt meter and it confirms what I thought. At idle voltage trickles down and stabilizes between 12.2-11.9v with headlights on voltage drops to 11.6-11.4 then if I turn on the fan with headlights on it drops to 11.2-11.0v. This is w/o my stereo on. Took it back to be retested with the new alternator and got the same result as before when idling. Shop guy said it was basically not producing anything at idle but I was getting 195amps @ 2000rpm. All these tests were done w/o any aftermarket stereo gear in the vehicle just stock electrical loads. I have to be missing something??? or got a defective new alternator. Any help is much appreciated.