It sounds like a stuffed AFM to me, but im no mechanic. Do a search here on AFM's see if you have the same symptoms. Also if the K&N filter is a oil type that wouldnt help. AFM's cost about $180ish from Subaru.

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Quickest Pig in Perth

x2 on air flow meter, the oil from the k&n pod has killed it, replace before your engine goes bang

Some my99's won't run well with a CAI.

Ask DAMO.

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nooooooooo i dont want my car to die D: so i should order a new afm and airflow box and get a good pannel filter yes?

I dont think ive seen anywhere about them running lean and cause the car to jerk purely because of a pod filter installed because of 'extra air'. Thats what the AFM is in there for What mechanic did you take it to? Do a search through here for reputable mechanics that are recommended to work on WRX's , and see what they say.

How well does it idle?

I was under the impression that a screwed AFM would mess the idle around, but through acceleration would be fine. It would just make your car run lean and boom!

In any case, if it were me i would try a new AFM (cheap compared to a motor rebuild!), and if that sorts it, all well and good. But I run a K&N pod filter (it was already installed when i bought it) and Ive had no trouble with it. From reading a lot of threads about it, the K&N filter should be fine, as long as its not over oiled. Perhaps even buy the oiling kit yourself, and give the filter a clean and lightly oil it yourself if youre not sure.

buy an apexi powerintake dry pod, they are heaps better for the afm than any oiled filter

so i should get the apexi dry pod and mount it under the guard so it doesnt get hot air hey? sounds good haha but i will have to get my ecu upgraded wont i or will it be okay?