On starting the car, 93 WRX first thing in the morning [kept in garage] the revs hunt like mad, going from about 1300 down to about 400 RPM then back up, if you help the revs by holding them about 1500 for 90 seconds or so then lift off the revs hold at about 1300 until the car warms up, apart from that the car is fine. Fitted with HKS green mushroom filter & HKS drain pipe for an exhaust, these have been on the car for sometime.

Any suggestions ??

 

Idle valve maybe?

Failing that, probably the fuel/air flow sensor I would guess. Should show up pretty quickly on a Subaru test rig at a dealer.

Richard

 

Could be your MAF on the way out ( Mass Air Flow sensor )

Tim

 

Almost definately one of two things. As mentioned already it's quite likely that it's the MAF sensor. This may not show up on the select monitor but is worth checking. Other thing is small hole or split in one of the boost pipes. You should also check the intercooler piping for cracks.

Paul.