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Old 01-29-2020, 04:48 PM   #3
Scooby Specialist
Member#: 419354
Join Date: Apr 2015
Chapter/Region: MAIC
Location: Newark, Delaware
2007 STI
Crystal gray metallic


1. Yea, sounds like power steering. Check fluid level noting the hot & cold fill lines on the reservoir. If at the correct level, while idling, pop the hood and remove the power steering reservoir cap and see if the fluid appears foamy or has bubbles. There’s an o-ring between the suction tube & where it connects to the top of the power steering pump that likes to let air in; it needs replacement periodically. If you replace it take care not to over-torque it.

Another cause could be an incorrect hose is installed. The tube between the reservoir & pump is under suction and therefore needs to be rigid. If heater or other flexible hose is used, the tube will collapse and restrict flow to the pump. If it’s easily compressed by hand replace it with OEM part, which has a distinct formed shape.

If it’s neither of these, internal pump seals could be letting go or the steering rack might be leaking. It's also possible an undersized or poor quality aftermarket pump is installed.

You can bump the base idle 100 rpm without hurting anything, but it’s a band-aid. You really need to investigate pump/ leak issues.

I’m pretty sure the 09 WRX is drive by wire (electronically controlled w/o a throttle cable). If this is the case there is no IAC valve to clean; removing & cleaning the throttle body & butterfly plate is usually beneficial and worth the effort though.

2. I use Motul as well. I see no issue with Mob 1 though.

The OEM filter is actually pretty good, that's what I & many others use. There’s a nice comparison to aftermarket filters somewhere here on the forums. From it, I recall Bosch and the top tier Purolator (gold?) being equivalent or slightly better alternatives.

3. Mark it with whiteout before disassembling and put it back exactly, or Google search the Factory Service Manual (FSM) which will outline the procedure in detail - it’s readily available & super easy to find.
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