Ive got about 22500 on my 04 wrx, no mods. Ive noticed recently that when im sitting at a traffic light after the car is warmed up that sometimes, and seemingly randomly, the rpms will fluctuate about 150-200 rpms and the car will almost stall out but the catch itself. It seems to be happening more and more lately. I am planning on bringing it into the dealer since im still under warranty. Just wondering if anyone else has had this issue and if so what it ended up being. Thanks

 

I tried searching the forum but didn't find anything. I haven't had this issue with my car. I would take it in and get it checked out.

 

I'm not exactly sure if this would cause your problem, but have you changed your fuel filter since purchasing the car? I think the maintenance schedule calls for a replacement of the fuel filter every 15k miles.

 

The rpms fluctuate a bit for me(at idle/stop) when the defroster is on. It goes away when its off.

Fuel filter isnt until 30K

 

It does that because your a/c is running...

 

nope..not running ac during the winter. I was thinking that it might be while the heater was on for defrosting. But I tried turning off the defroster this morning and it was still doing it. Im not incredibly worried about it, just want to get this resolved before the warranty runs out.

 

When you run the defroster the a/c compressor runs because a/c air isn't humid so it defrosts better, but the heater doesn't use the compressor... I still think it's the fuel filter, but I'm not sure if this'll help but try reseting the ecu and see if iti still does it.