When my car is idle at a stop light or in my drive way. The rpm's tend to drop and go back up. it does this frequently. Some one told me it might be my alternator?

 

could be a vac leak as well. how much do they drop?

 

well it idles at 1K normally and then drops maybe .3k lower

 

does it surge, what mods do you have if any? also do you have a tune?

 

i have a esplir jgt 500 exhaust, custom downpipe, 02 dump, k&n intake, custom intercooler, ets licp, forge mbc, and ya im tuned pushing 24 pounds of boost

 

ok, i would check for any leaks and also test your battery and alternator. you could be due for a tuneup as well.

 

Could be your fan starting. Evo alternators are pretty small and the batteries aren't the best. Basically, as long as the car stays running, I wouldn't worry about it.

 

Probably your fan coming on.

 

When you got tuned last what did you set your idle to? If you didn't adjust it at all I would recommend that. I bumped mine to 800 or so to accomodate for my cams. It made a world of difference.

...although with the A/C on at a stoplight my RPMs are all over the place....way too low and threatening to stall.

So my advice is to try bumping up your idle to 800-900 and see if that holds it steady. The normal fan won't impact that....but with A/C it will.