good idle, running bad...wtf

[HKsilvia]

3 days of searched plus 3 hrs sleep per night due to work doesnt seems to help so im begging for some help.

SR engine, been swapped for year already and doesnt seems to have any problem. recently it starts giving me symptoms, last months while i was driving on freeway it chocked on me once. just like the car is running out of fuel for 1 split second. (i still have half tank) at first i thought the road was bumpy and the coilover causing some wheelhoppin so i didnt pay much attention. however, this "chocking" symptoms starts appearing more and more frequent, at first it only happens on freeway, but then it starts happening on low speed local driving. i decided it is not safe the drive it around so i leave it for 2 nights. 2 days after, i started my car, the car cant idle anymore, i rev the engine and the car barely response my right foot.

so i took it to the shop, their answer is im having a vacuum leak and charge me for $45, i got my car back the same day and its run fine, idle ok, no "chockin" issue until the next day, which is today, this shit came back again!!! even though idle is still fine, but "freeway chockin" definitely driving me nuts.

so with all the common sense and all the searched i had come over so far i would say it is something with the fueling system, especially fuel pump and fuel filter (lets hope the fuel lines are ok). however there is only one thing in my mind... if im having problem with fuel system (hopefully) why my idle can be so stable, shouldnt it be rough? i even rev the engine and it didnt shows any bogging/hesitating.

am i in the right direction? or is it possibly something else? im planning on buying a walbro 255 as replacment, but how about fuel filter? are all SR engine using the same filter as Z32 filter?? i dont want to spend money on the wrong stuff.

thx for reading, any help is appreciated.