Odd Idle? Sticks at 1,700 RPM now low under 1k RPM and wants to die?? TSI

[ECLIPSE95]

Ok I just bought my car a 95 TSI AWD and I took it for many test drives and ran fine..now that I have had the car for a day the idle is a little weird? and I was wondering how to fix it or where to start...

At first the idle stayed at 1,700 RPM after it has been warmed up...well it went away and now when I drive the car the idle is below 1k and sometimes at stop lights it pulses from 200 to 1k? the battery light flickers on when it gets down to the 200 RPM line then jumps up to the 1k again then the battery light flickers off? like it wants to shut off? it does this a couple of times then it idles at 700-800..then it goes back to normal..

Any Ideas?? I am need of some serious help..thankz

2 mods where put on this car..a K&N air filter and a crappy pacesetter turbo manifold that I am not too empressed with..just to let you know of the mods..but other than that it is completely stock..

 

[DSM90AWD]

Idle problems are generally a result of a bad/dirty ISC motor or a boost leak.
Did your car throw a CEL?

Are there any large exhaust leaks with that manifold?

 

[ECLIPSE95]

ya I guess the car has a bad instument panel..so it had a code for somthing to do with the fuel...I guess one of the injectors has some buildup and its malfuntioning..and the manifold leaks somewhat but not too bad...I might replace the ISC anyway to see if that helps..but thanks now I know where to start..~Dustin