Jerk, and Quick bucking 2002 Legacy GT Need Advice

[spank2798]

Hey guys. My car was throwing a P0420-Catalyst efficiency below threshold bank1--I then replaced the first o2 sensor with a Denso sensor. It then lead me to believe at 135k my cat was shot, I then replaced it..

I was also throwing a P0065-Air assisted injector control range/performance code..

I cleared the codes..The car CEL hasn't come back on but the car still acts as it was such as a quick jerk around 2000rpm and even at highway speeds in 5th gear when I go to give it gas it will jerk. To clarify, after I had the cat replaced with the new o2's today, the ride home was fine..then when I drove to school 2hrs later I get the same quick jerk..then I accel and shift, into the next gear and same damn thing happens...I am really at wits end..The car has 135k and is an 02 Legacy GT. I have heard it could be MAP or MAF sensor, which one do I have? I have bought CRC MAF cleaner but don't know exactly where it is located. Could it also be the throttle positioning sensor? Not sure where located.. I am about ready to take to the STEALERSHIP! but hopefully you guys can guide me..Thanks fellow SLI'ers!

[2000gtb]

MAF/MAS air should be right behind the Filter/intake.. but I dont think you have one(not sure???) there is an Intake air temp near your throttle body on that box where the filter sits.. check if your sparkplug wires are arching.. I had an experience where my wires are arching everywhere.. it felt the same as what you are talking about but I think its more like you loose power and all of a sudden you get a burst of power when the arching goes away..

Make sense??

[spank2798]

Hmm, spark plugs were replaced around 120k...but I guess it could be spark plugs..No Codes though..so not sure.

[blackstar]

do you have an cold air intake ? do you have a little black box / sensor behind the air filter box ? Is it a Manual/Auto ?
Usually 02's will have a MAP system, and only some have Intake air temp sensors.

When you did spark plugs - what kind ? pulling on the wires / boots you could have damaged/separated one of the wires internally, or your plug could have a small crack in the porcelain which sounds possible. At least pull them out look down the side of the porcelain, check the plug gap - check electrode, @ least make sure that you tightened them, re-torque em'.

The front sensor you replaced Subaru actually calls it the air / fuel ratio sensor, and the rear sensor is an Oxygen sensor, I know they are virtually identical, but the a/f ratio sensor actually reads at a much higher voltage. The Denso sensor, was it an OE connector or did you have to splice ? You may wanna consider doing the rear O2 just cause you just replaced your cat.

[spank2798]

Its a manual trans..the Denso front sensor was OE...again, after I changed the front o2 and the cat..it ran good..then started to buck around 2rpm. It's like a hesitation..Then the next day it drove fine..I had been driving it for a week and its been fine, now all of a sudden its doing the same problem. I don't think there is a MAF sensor because of the fact that there is nothing by the airbox..I do not have any intakes or mods..Its bone stock..I have already put close to $400 into the problem..Do you think at this point I should just get a diagnostic and see what the dealership says? Thanks for the input and slow response. I have been mad busy with school..

[harrymaneuvers]

This may sound stupid but check to make sure that your air filter box has the bottom tabs engaged into the other side of the filter box. I had a issue like this (except that it threw a couple MAF and injector codes) and it turned out that I didnt have the bottom two tabs inside the holders on the air box and it was causing all sorts of stuff to happen when it sucked air in through the gap in the bottom.


Anybody else thinking it is a fuel pump issue?


Does it seem like it is a fuel surging jerk or a driveline jerk?

[spank2798]

Definitely like a fuel jerk..meaning I give it gas and it will hesitate and buck hard..then kick back in and the rpms go up..wouldn't I have gotten a fuel pump code? I am about ready to bonkers!

[harrymaneuvers]

I would be suspect of the injectors or the fuel pump...


Have you ran any injector or fuel system cleaner through it?

[harrymaneuvers]

http://legacygt.com/forums/showthread.p ... ?p=1463440 (http://legacygt.com/forums/showthread.php/argh-p0065-killing-me-73529.html?p=1463440)

[harrymaneuvers]

http://legacygt.com/forums/showthread.p ... ml?t=91247 (http://legacygt.com/forums/showthread.php/symptoms-failing-fuel-pump-91247.html?t=91247)

http://forums.nasioc.com/forums/showthread.php?t=257835

Good reading info for you.


So it seems like there is a very real possibility that it is actually the air filter box not being correctly reassembled. It could also be a clogged fuel filter or finally a bad fuel pump.


The good news is that it looks like there are plenty of people who have experience this issue.

[spank2798]

Update! I took it to the dealer...he said exhaust leak..fixed that..then beat up fron o2 sensor..replaced..he drove it for 5 miles.. I paid and left...no more than a mile down the road from the dealership, the crap starts again! He did tighten airbox also...So that cost me $277.00..and the car runs a little better but still same jerking...I took it back, he drove it with me and we noticed the issue..Bottom line I'm bringing it in for diagnostics on monday...they said they would cut me a break..that will happen when hell freezes over! So, I appreciate the input, but if the Subaru mechanics are dumbfounded then I don't know what to say..

[spank2798]

Wow! Further update..So I double checked what codes I was throwing on an old piece of paper..so happens that one of them was the infamous p1507--Idle speed control AKA idle air control valve..so I went to autozone and paid $2.00 for carb cleaner, cleaned the crap out of the IACV and voila! The IACV was gummed up pretty bad! Car is running like a top!

[harrymaneuvers]

Funny thing is that I almost posted about the MAF or IACV but realized that I didnt when I posted something else on the subject.

Good to hear you got it figured out.

[spank2798]

Yeah..Thanks for the input! I hope the car stays this way!