Topic: Bogging/bucking and loss of power at low RPM.

[Way-do]

I have my suspicion as to what needs replaced, but I'd like to check the community brain before I buy the part.

The Car:  2001 2.5 RS  5MT, 166000km
Mods: Delta 1500 Cams, OBX Header w/ welded in Magnaflow cat., Stromung Muffler, Cobbled together short ram intake.

Plugs and wires are newer. Replaced Idle Control valve with spare (no change), Front O2 is newer (prev owner around 120Kkm). All above mods completed at 160000km and it was running fine up until a couple weeks ago. Had initially thrown P0420 but that went away. NO evidence of vacuum leaks. Currently no codes.  No missfires.
(Have spare fuel pres regulator, compete rail and injectors, Map Sensor, TPS, 07 for parts and an OpenProt1.3 that I have to get around to learning how to use.)

The Problem:
INTERMITENT

At low rev/ high loads the car had no power and almost stalls.  Ocasionally going up a long hill I'll go up to fourth and as the clutch comes on, I can fell there is NO power and have to slip the clutch to get the revs up and keep it going with traffic. Occasionally, getting going from a light up a bit of a hill, it just gets going and then hits a wall. Then I have to clutch and rev the hell out of it.  When cruising in high gear, there is a spot where decresasing throttle a spot about 1/6th throttle seems to have a weak spot.  The worst area seems to be around 2500-3000rpm at low throttle.

Idle:  The idle is all over the place.  It is rough, it will drop to 500, near stall, the bounce and recover to 1500-2000 but sputtering and missing all along.

High End:
Great.  At about 4000RMP, where there is a normal bump in the torque curve, there is now a big bump and everything smooths right out.

I appreciate all suggetions. Thanks for your time.

Wader

[KLZCYA]

Sounds a hell of a lot like when my coils get wet. Not sure what NA is like/how it is set up, but are you sure the coils are good?

Mine bucks and is a real pain in the assay to drive after letting it sit in the rain for too long. Clears right up after it warms up. Just something to think about.

[Way-do]

Thought about it.  It started during monsoon season in Calgary, but has not gone away.  I'd also expect it to cause a missfire, and be less throttle angle dependant. 

[Zac]

coil back or a faulty plug wire

[Way-do]

Will throw the spare plug wires on just for fun.

New Throttle posn sensor makes it WAY better, but is not the root cause... Still did it once off the line last night.

Can't wait to get this thing hooked up to a computer to see what is going on.

[AWDFTW]

There is an issue with some where the knock sensor is triggered by low rpm engine vibrations and retards timing 10* from 1500-2500rpm. I have this issue with my 2.2L.

[Way-do]

So using ECU Explorer, I discovered that it is dumping all timing to the point of +10TDC which is where all the power is going.
This led me to logging knock.  Sure enough, it knocks... a lot. In turn, it retards like crazy.
Why?  Look at Front O2, it's purring along close to one, hunting a bit, but not bad.
Suspect it's running crazy lean, replace fuel pressure regulator, no change.
Plumb in a temporary fuel pres guage, steady and smooth.

-scratch head-

Realize that the bump at 4000rpm is the switch to open loop, as is the burble WRT throttle position.
Unplug O2 sensor.
Car runs tollerable well, but doesn't throw a code, or really seem to care.

Replace front O2 sensor. All is well.
Have a beer.

[vaportrail]

Thanks for this thread, my 2.5 was doing the exact same thing, saved me a pile of money trying to figure out what was wrong! I also found this thread, with some decent pictures, in case anyone needs to do this also.
http://www.clubwrx.net/forums/maintenance-service-repair/134287514-diy-front-o2-sensor-02-wrx.html

[Way-do]

Glad I could help.  That's quite the DIY.

Mine is as follows (you may need to remove some intake ducting):
-Open hood. Look straight down from cruise diaphragm.
-Unplug sensor by flipping up white bit. Unwrap wire pig-tail twist tie unit.
-put your 02 Sensor socket on a really long extension
-place O2 Socket on sensor, turn counter-clockwise.
-Put a tiny bit of anti-seize on all but last thread of new sensor.
-thread into header by hand until snug.
-Put socket onto sensor, turn clockwise.
-plug in.
-reset ECU
-Beer

[vaportrail]

I did actually have to change it up a bit, those pictures were more of a rough guideline. I pretty much followed your steps except I couldn't seem to get my O2 socket to fit with a ratchet on it, so I improvised with my 22mm wrench. I can't reset my ECU yet either, don't have the ECU computer. In any case, the car is running much better now!

[darthekai]

Sorry for resurrecting a dead topic and i just noticed buddy got banned, but it fits the topic pretty well...
Klzcya said something about this and I was Just wondering if an one could clarify..
My car sometimes sucks for what he describes and boggs and jumps around when starting from a stop and it seems to get better with heat.. To me it almost feels like a clutch issue with it cycling catching and slipping.. but no matter how gently i let that thing out when it's raining i get this horrible shaking and bouncing around. Also my car reacts kind of poorly to rain (my theory is that my engine block is actually made of sugar)  but the clutch seems quite strong under heavy load once I'm moving...

Anyways let me know if this sounds like the same problem to anyone.  Also whether or not you think replacing the coil  pack would solve it.. I got a coil pack off ebay for 40 bucks because it seemed like a smart thing to do but it turned out to be the wrong one (too many holes and not enough connector pins).