just purchased 2000 impala ls w/ 100k

I have just purchased a 2000 ls impala w/ 100k miles. I will be asking for advice/suggestions on many issues but one is the fact that warm or cold (w/ no accessories on), when it is idling you can hear the engine going back and forth dipping (almost like a struggling sound) and then it goes back to normal.
The rpms are fluctualting between about 6-700 to about 1100. I was wondering if anyone can tell me if this is normal or what it could possibly be. I'm hoping at most it is an alternator problem.
Thanks in advance-Tim

Im not a mechanic.Im just a guy who has had a lot of vehicles and alot of vehicle problems and i drive over 50k ayear.I think your problem sounds like a vacuum leak

actually its a common thing for the impalas, everyone ive spoken to notices it. mine doesnt do it in that same range. mine does it at like 600 - 800, its just the idle. you could try using seafoam, that helps the idle out quite a bit. you can pick up a can at a local auto parts store(autozone) and there are instructions on the can.
and actually, when I went from unleaded to preimium, I noticed it went away, almost. its still there VERY VERY little, but using premium helped it too. its only about a $3 difference than regular.

My 3.8- 01 with 163k idles perfect. It does not surge at all maybe some do and some dont. And what is this sea foam stuff supposed to do?

its a cleaner, you can put in in your gas tahnk, oil (last 500 miles before oil change), pretty much anywhere in the car to clean out all the carbon build up and dirt and whatnot.

some people have had DTC codes and used seafoam and walla, dtc was gone, just by cleaning out parts. the stuff works wonders.

Thanks for the responses,I'm glad to know it is not anything costly. By the way my dex-cool is looking pretty bad,(after I filled it with the havoline considering there was none to speak of when I got it and the light was on) -I was wondering considering I'm in Ct and won't be able to flush it myself for a good couple of months, I was wondering if I should have it flushed and filled at the dealer($185 including the tax and therm. change), compared to midas or something for less than half. I just wanted to get some opinions.
Thanks-Tim

In addition to a possible vacuum leak you could have a defective or dirty idle air controller (IAC). The fluctuating rpms and idle above 1000 rpm is a symptom of an IAC. Also, you could remove the IAC and carefully clean the spring loaded pintle with carb/throttle body cleaner and where it mounts to the throttle body, especially the air orifices. A defective IAC will also make it sound like the engine has a vacuum leak. This is applicable to the 3.4L or 3800.

yeah, you can use the seafoam for that too. I havent done it, but others have somehow cleaned out there intake with it. or just buy the carb cleaner like he suggested.

yeah, you can use the seafoam for that too. I havent done it, but others have somehow cleaned out there intake with it. or just buy the carb cleaner like he suggested.

Seafoam is good stuff. For the engine treatment, the best way to use it to clean the throttle body is through one of the vacuum lines while engine is running. The directions have the recommended procedure. Plus Seafoam tranny treatment will do wonders to free up sticky solenoids in the tranny and valve body. I noticed Autozone is carrying the stuff, whereas I used to get it from NAPA.