'08 2.5i lerching during braking

I am having an odd lerch when braking from around 35 to stopped. It feels like the engine is still getting gas during the stop. It also happens when I slow to just a couple mph to pull into my driveway. The problem seems worse when the car is fully warmed up.. The car is a 2008 Legacy 2.5i limited with an auto transmission. The car only has 36k on it. I have replaced front and rear diff fluid. I will be changing the tranny oil this weekend. I have inspected the brakes and abs lines, nothing out of sorts. Struts are still in good shape.

 

Has anyone had this issue?

Any advice would be greatly appreciated.

throw it into neutral when youre slowing down and watch the engine rpms. it should drop right to idle and stay there. if rpms fluctuate then chances are the throttles not closing all the way.

 

these cars are all fly by wire, meaning theres no mechanical connection between the gas pedal and the engine, its all done with sensors and servos. unplug the sensor on the pedal and gently clean the contacts with come electrical connector cleaner. CRC makes a good one you can find at any local auto parts store. sometimes water and salt can get in there and cause the sensor to fritz out once in a while. also, remove the intake boot and inspect the throttle plate. if theres any black gunky shmagma anywhere near it, clean it all off. carbon buildup like that can keep the throttle from closing completely.

 

You may also want to clean the contacts in the connector on the throttle body as well.

Thanks for the input. Ill add your suggestions and a maf cleaning to my to do list for this weekend.

Do subarus have a throttle position reset procedure?

I tried throwing it into neutral. The problem went away. Is this still pointing to the throttle body or possibly something else?

it all depends on what the throttle is doing when youre slowing down. do you have an iphone? if so download the "GoPoint Technology" app and purchase the OBD II cable. it allows you to monitor just about all of the cars sensors via the OBD plug using your iphone. (or other smartphone too i think) you can visually see what most sensors are doing and beats using a voltmeter any day haha.

 

If it went away in neutral, then clean out the throttle plates and sensors this weekend and repeat the tests. its best to do one at a time and then repeat the tests instead of multiple fixes at once. mostly for future reference. as far as a throttle reset procedure, ive never heard of one, but maybe someone else can chime in and fill us both in haha

 

how violent is the lurching? can you replicate it in any gear when slowing down?

Thanks again for the input. I'm android, but ill check out that app and try to find a miniusb to obd2 cable (or make one).

 

I used to be a nissan guy, and they have a tps learning procedure. Didn't see anything in the fsm. Was wondering if I could turn the key 1000 times and stomp the brake pedal until my foot goes numb.

In response to the last line. The lurching isn't severe, but is noticeable by all passengers. You expect to come to a complete stop, but the car feels like the engine is still racing or the abs is engaging. The car stops then you can feel the momentum still push forward.

i think i can rule out the abs as an issue. if it were engaging as the vehicle stops, you would feel the feedback in the brake pedal as the abs solenoids pulsate. I wont be able to say much until after i know what happens when you finsh your "to do" list haha.

 

Automatic transmissions have a feature called "converter lock." all that means is the torque converter will physically lock the inner hub to the outer casing at highway speeds. its *supposed* to unlock when you come to a complete stop. its possible, but unlikely, that the converter is locking and unlocking itself instead of staying completely unlocked when you are at a stop. you will feel the locking and unlocking as the lurch youre describing. if the transmission is in neutral, no power will flow to the wheels and you wont feel it. however, all the other possibilities have to be eliminated before i jump to a comclusion and say your tranny needs work.

 

The only way to confirm the converter is locking ang unlocking correctly is with a factory scan tool that will allow access to the transmission control module.

I cleaned the mass air flow sensor and all connectors. The throttle body was pretty clean, but seafoam spray cleaned it anyway. I didnt get to changing the tranny fluid. Will do that on wednesday.

 

Problem still persists.

hm. Haven't seen the breaking issue, but man when I hit third it doesn't matter if i'm on it or just cruising it has a noticeable jump to it.

Hmm, it could be a vacuum leak, I've see this happen before with a vac leak.

 

-Mike Paisan

 

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The car runs noticeably smoother since the small amount of maintenance. The throttle reponse is also vastly improved. The problem still persists. I will check the vac lines when I change the tranny fluid.