2000 Outback engine bucking

[thatsallfolks]

Hi all. This is my first post, so I'll try not to commit any faux pas.

 

I have a 2000 Outback I bought new. It has the 2.5 liter phase 2 engine

with an automatic transmission, and about 49,000 miles on it now.

 

For several months it has been running wrong. Sometimes it hesitates from

a stop, or slow start; sometimes it idles rough. But the worst is a

bucking/jerking that takes place on deceleration. It happens somewhere

between 30 and 40 mph and the tach is around 1500 rpm. Deceleration can

mean coming off of a freeway ramp from 70mph, or just slowing from 40-45mph.

It's unpredictable, and intermittent. And by bucking/jerking I mean the car

will do this until speed drops below 30mph. So it will jerk back and forth

maybe 30 times. It is not a one time jerk like a hard downshift.

 

Anyway, I have seen lots of stuff on hesitation and rough idle, but what

about this bucking thing? So far, the dealer has replaced the rear O2

sensor, the vent valve by the gas tank, and re-flashed the ECM. As a stab

in the dark, they also cleaned the throttle plate. As my own stab in the

dark, I replaced the fuel filter and the PCV valve, and tried some fuel

system cleaners.

 

Nothing has changed. Has anyone had a similar experience? Has anyone fixed the problem? I'd appreciate any help.

 

Thanks.

[99obw]

That's a tough one without riding in the car.

 

IIRC the Phase II's came with champion copper plugs from the factory. Have the plugs been changed? I would pull a plug and take a look. My preferred plug for these engines is NGK laser platinum.

 

Also take a look at the air filter.

 

When I hear hesitation/rough idle/bucking one thing I think of is carbon accumulation in the cylinders. I think a seafoam treatment is worth a try. OTC injector cleaners don't work very well at removing carbon. Seafoam is pulled directly into the intake via a vacuum line and allowed to sit in the cylinders for a little while, so it's very effective. Do a search and you will find plenty of information detailing it's use. Make sure you change the oil immediately after using the seafoam. You may get a MIL due to misfire.

 

A little off topic but relevant:

 

My '01 Jeep had a persistent rough idle when cold. The dealer changed the fuel pump, plugs, and performed a fuel injection cleaning. I then found a TSB on cold start rough idle and had the PCM reflashed. Nothing made it any better. Then I tried seafoam. WOW! Ran like new, but the rough idle came back within a week. I had tried techron and other fuel injection cleaners but they did nothing. Now I use a product called Fuel Power in every tank. It improves MPG enough to pay for itself, the rough idle is gone, and the fuel system and cylinders are presumably spotless. Our suby responds very well to the FP, with mileage in mixed driving consistently above EPA highway.

 

The general aim of my post is that the often forgotten maintenance items should be verified before sinking any money into hard to diagnose symptoms.

[slo5oh]

Hi all. This is my first post, so I'll try not to commit any faux pas.

 

I have a 2000 Outback I bought new. It has the 2.5 liter phase 2 engine

with an automatic transmission, and about 49,000 miles on it now.

 

For several months it has been running wrong. Sometimes it hesitates from

a stop, or slow start; sometimes it idles rough. But the worst is a

bucking/jerking that takes place on deceleration. It happens somewhere

between 30 and 40 mph and the tach is around 1500 rpm. Deceleration can

mean coming off of a freeway ramp from 70mph, or just slowing from 40-45mph.

It's unpredictable, and intermittent. And by bucking/jerking I mean the car

will do this until speed drops below 30mph. So it will jerk back and forth

maybe 30 times. It is not a one time jerk like a hard downshift.

 

Anyway, I have seen lots of stuff on hesitation and rough idle, but what

about this bucking thing? So far, the dealer has replaced the rear O2

sensor, the vent valve by the gas tank, and re-flashed the ECM. As a stab

in the dark, they also cleaned the throttle plate. As my own stab in the

dark, I replaced the fuel filter and the PCV valve, and tried some fuel

system cleaners.

 

Nothing has changed. Has anyone had a similar experience? Has anyone fixed the problem? I'd appreciate any help.

 

Thanks.

You bought it new. Take it back to the dealer and MAKE them give you a rental while they fix it. That way they will get to work on it FAST. I've seen mustangs have that problem... it's usually a bad Throttle position sensor (TPS). Could also be some goo on your MAF contacts.

[thatsallfolks]

Hey, thanks for the replies. The dealer does have the car now; they're trying to reproduce the problem. Depending on what they come up with, I plan to show them your comments, 9obw.

I'll let you know how this plays out. Hopefully it'll have a happy ending.

[slo5oh]

That's a tough one without riding in the car.

 

IIRC the Phase II's came with champion copper plugs from the factory. Have the plugs been changed? I would pull a plug and take a look. My preferred plug for these engines is NGK laser platinum.

Copper plugs work better, they always will provide a better spark, but they won't last 100k like platinum. That's the reason dealers have gone to platinum. Just because it lasts longer doesn't mean it's better. My cars will always get copper.

 

When I hear hesitation/rough idle/bucking one thing I think of is carbon accumulation in the cylinders. I think a seafoam treatment is worth a try. OTC injector cleaners don't work very well at removing carbon. Seafoam is pulled directly into the intake via a vacuum line and allowed to sit in the cylinders for a little while, so it's very effective. Do a search and you will find plenty of information detailing it's use. Make sure you change the oil immediately after using the seafoam. You may get a MIL due to misfire.

I agree that carbon build up can cause lots of problems. I've seen a different product that worked similar to the seafoam you are describing, it plugged into a vacuum line and sucked a bottle dry in about 5 minutes causing the exhaust to blow nasty smelling white smoke, but once done the car that was hardly idleing now had a steady idle and ran a lot more smooth. I've seen old racers do this using a 50/50 mix of brake fluid and water pouring it slowly down their carbs. I'm sorry, but carbon buildup should not occur that fast. At 30k you should have very little carbon buildup, 60k will have some... now at 100k you will have enough that it may start causing problems. I run about 1/4 bottle of redline fuel system cleaner (added to a full tank) every 30k 50k just to keep everything clean since I run the cheapest gas I can find.

 

A little off topic but relevant:

 

My '01 Jeep had a persistent rough idle when cold. The dealer changed the fuel pump, plugs, and performed a fuel injection cleaning. I then found a TSB on cold start rough idle and had the PCM reflashed. Nothing made it any better. Then I tried seafoam. WOW! Ran like new, but the rough idle came back within a week. I had tried techron and other fuel injection cleaners but they did nothing. Now I use a product called Fuel Power in every tank. It improves MPG enough to pay for itself, the rough idle is gone, and the fuel system and cylinders are presumably spotless. Our suby responds very well to the FP, with mileage in mixed driving consistently above EPA highway.

 

The general aim of my post is that the often forgotten maintenance items should be verified before sinking any money into hard to diagnose symptoms.

Sounds to me like your jeep has other problems. I would let it run normal until it's got the rough idle then check the cyl pressure on each cyl. You probably have one bad or leaking injector that's causing the extra carbon buildup.

[rweddy]

Hi all. This is my first post, so I'll try not to commit any faux pas.

 

I have a 2000 Outback I bought new. It has the 2.5 liter phase 2 engine

with an automatic transmission, and about 49,000 miles on it now.

 

For several months it has been running wrong. Sometimes it hesitates from

a stop, or slow start; sometimes it idles rough. But the worst is a

bucking/jerking that takes place on deceleration. It happens somewhere

between 30 and 40 mph and the tach is around 1500 rpm. Deceleration can

mean coming off of a freeway ramp from 70mph, or just slowing from 40-45mph.

It's unpredictable, and intermittent. And by bucking/jerking I mean the car

will do this until speed drops below 30mph. So it will jerk back and forth

maybe 30 times. It is not a one time jerk like a hard downshift.

 

Anyway, I have seen lots of stuff on hesitation and rough idle, but what

about this bucking thing? So far, the dealer has replaced the rear O2

sensor, the vent valve by the gas tank, and re-flashed the ECM. As a stab

in the dark, they also cleaned the throttle plate. As my own stab in the

dark, I replaced the fuel filter and the PCV valve, and tried some fuel

system cleaners.

 

Nothing has changed. Has anyone had a similar experience? Has anyone fixed the problem? I'd appreciate any help.

 

Thanks.

Is the car still under factory warranty?

 

The reason I ask this is because dealerships are terrible at troubleshooting issues. They are parts swappers and are horrible at finding issues. They will just keep throwing parts at it until it is fixed. Now if it is under warranty then let them!! If you have a local Subaru specialty shop that is such a better way to go than the dealership.

 

my .02

[99obw]

Copper plugs work better, they always will provide a better spark, but they won't last 100k like platinum. That's the reason dealers have gone to platinum. Just because it lasts longer doesn't mean it's better. My cars will always get copper.

I agree that on paper coppers should be better, but I don't think the average driver will ever notice the difference. I think for most folks who have someone else do the work platinums are more economical.

 

I agree that carbon build up can cause lots of problems. I've seen a different product that worked similar to the seafoam you are describing, it plugged into a vacuum line and sucked a bottle dry in about 5 minutes causing the exhaust to blow nasty smelling white smoke, but once done the car that was hardly idleing now had a steady idle and ran a lot more smooth. I've seen old racers do this using a 50/50 mix of brake fluid and water pouring it slowly down their carbs. I'm sorry, but carbon buildup should not occur that fast. At 30k you should have very little carbon buildup, 60k will have some... now at 100k you will have enough that it may start causing problems. I run about 1/4 bottle of redline fuel system cleaner (added to a full tank) every 30k 50k just to keep everything clean since I run the cheapest gas I can find.

I think it depends on the quality of gasoline, the presence of oxygenates, and driving style/pattern.

 

Sounds to me like your jeep has other problems. I would let it run normal until it's got the rough idle then check the cyl pressure on each cyl. You probably have one bad or leaking injector that's causing the extra carbon buildup.

I think you may be right. I had given some thought to a stuck/leaking injector. The plugs look perfect when I pull them and mileage is right on target though. I think the problem is intake valve deposits and I just need to get them cleaned and keep them clean. I will run a compression test when I get a chance. I am going to have the oil analyzed at 7500 miles and look for fuel dillution.

[thatsallfolks]

Well, the dealer finally found the cause; it was the air-fuel mix sensor. Once they replaced that, the car drove like new. I'm pretty confident in the repair at this point because it's been about 3 weeks now, and we've had no sign of the earlier problems reappear. It took the dealer maybe 10 days to actually find the problem; I drove a rental the whole time they had my car. But Subaru paid for everything. Needless to say I'm happy with Subaru and the final outcome.

 

So, if anyone else out there is experiencing similar problems, have the dealer check the air-fuel mix sensor; it just might be the culprit. I hope this experience winds up helping someone else too.

[friendly_jacek]

Well, the dealer finally found the cause; it was the air-fuel mix sensor. Once they replaced that, the car drove like new. I'm pretty confident in the repair at this point because it's been about 3 weeks now, and we've had no sign of the earlier problems reappear. It took the dealer maybe 10 days to actually find the problem; I drove a rental the whole time they had my car. But Subaru paid for everything. Needless to say I'm happy with Subaru and the final outcome.

 

So, if anyone else out there is experiencing similar problems, have the dealer check the air-fuel mix sensor; it just might be the culprit. I hope this experience winds up helping someone else too.

Are you describing the A/F ratio sensor (aka lambda aka front O2 sensor)?

If so, did you have engine light?

[WAWalker]

Considering that there was a recall on the Air/Fuel ratio sensor in 2000.......................wouldn't trust that dealer with any work you have to pay for. What took 10 days should have took 10 minutes, to log on and punch the VIN into the computer:-\

[thatsallfolks]

Yes, they said it was the A/F ratio sensor. No, the engine malfunction light was not lit. But it was lit when this whole thing started last spring. So back in June, based on the engine error code, they replaced the rear O2 sensor. I wonder why they never considered replacing the front one (I assume that's aka the A/F ratio sensor), especially when the problems persisted?

 

Anyway I didn't know about the recall. It really did seem like a lot more hassle than it should have been. I can only say I'm glad it's over and the Outback is running well again, and Subaru picked up the tab (of course, if it was a recall item, they would've had no choice anyway). And thanks for all the input.

[HAGENDAS]

Well, the dealer finally found the cause; it was the air-fuel mix sensor. Once they replaced that, the car drove like new. I'm pretty confident in the repair at this point because it's been about 3 weeks now, and we've had no sign of the earlier problems reappear. It took the dealer maybe 10 days to actually find the problem; I drove a rental the whole time they had my car. But Subaru paid for everything. Needless to say I'm happy with Subaru and the final outcome.

 

So, if anyone else out there is experiencing similar problems, have the dealer check the air-fuel mix sensor; it just might be the culprit. I hope this experience winds up helping someone else too.

I am having the same symptoms in my 00 2.5rs and we are replacing the air fuel sensor. This just confirms our diagnosis.

 

thanks