Vibration when accelerating

I don't think this one is unbalanced tires, but I've been wrong before.

Last week my 99 automatic forester started vibrating when I accelerate. The first time I felt it was getting on the highway at the bottom of a large hill, trying the get up to speed the car was shaking a lot. I also feel it when I'm braking, but that might be due to some warped rotors. I started noticing it more and more after that. Today shortly after I left work the engine about cut out when I was coming to a stop. It felt like it feels when you forget to take your manual out of gear while coming to a stop. I slipped it into neutral and it kept running. Just the 'normal' shaking the rest of the way home.

I had the tires rotated 2 weeks ago, before going on a 4000 mile trip. No problems other than an annoying pull to the right.

Any ideas? It safe to keep driving, or am i killing it?

Charlie.

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Well, here is a quick list off the top of my head. Can't say if you're "killing" your car or not without a proper diagnosis of the problem.

You just had your wheels rotated? Did the shop tighten the lug nuts to the proper torque? Too much may cause rotor damage or stripped threads. You might check for loose lug nuts. Even competent people overlook things once in a while.

Have you checked your CV boots, inner and outer on both sides of the front, for possible splits and flung grease?

Bad wheel balance, dented rim, or maybe a rock or other foreign object in the tread? Rare, but sometimes a wheel balance weight can come off.

Checked tire pressures lately? Might also check for tread separation. Are all tires the same make, model, and have rolling circumference within 1/4"?

Could be rotors, if they have gotten so bad as to be rubbing things when not applying the brakes.

Front differential? Maybe check your oil level there.

Worn / missing suspension bushings?

Bad struts?

~Brian

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tsii wrote:

I doubt anyone here can tell you if its SAFE or not, if it is in danger of stalling - that is a safety issue to me. It definitely sounds like you have 1 or 2 real problems though. Do you detect any 'jerky' vibration maneuvering in parking lots? Is the check engine light on? Do you have a dealership or mechanic you trust to check it out?

Carl

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Random ideas to augment what's already been said: misfires, not yet numerous enough to trigger a check engine light

worn motor mounts combined with the above would produce some noted movement.

How do you feel the shaking? Stuttering stumbling acceleration? As though teh engine is vibrating excessively? In your hands from the wheel?

-- Todd H. 2001 Legacy Outback Wagon, 2.5L H-4 Chicago, Illinois USA

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I failed to mention the Engine Light has been on for a year, due to exhaust sensor (P420). I have the leak fixed, but it the light still comes one. I haven't read the codes since the new problem started.

The vibration seems to becoming from the engine on acceleration and form the steering wheel while braking, unless the engine down shifts in which case I feel both.

This is my first Subaru and I've already put 100k on it, total 140k. How many miles do these things get before the engine or transmission go out? I'll check the plugs in the morning and take it the mechanic if I can't find anything.

Thanks for the replys, - Charlie.

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Um... I'm gonna go out on a limb here and suggest perhaps reading the codes. Betcha got a sensor problem and or a misfire code awaiting you.

Warped rotors are the most likely cause of the the braking pulsation. Causes include numbnuts using torque wrenches without torque sticks at tire and brake places, and/or machining rotors -- it just seems to happen.

With all due respect, it sorta depends on--among other things--how long the nut that holds the wheel ignores check engine lights.

Best Regards, -- Todd H. 2001 Legacy Outback Wagon, 2.5L H-4 Chicago, Illinois USA

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snipped-for-privacy@toddh.net (Todd H.) writes:

Doh--meant to say "impact wrenches"

-- Todd H. 2001 Legacy Outback Wagon, 2.5L H-4 Chicago, Illinois USA

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tsii wrote:

Could be some engine misfire codes and also somecode related to a sensor, MAF or maybe IACV or ?

And the brake rotor issue is a good one to look at for the vibration on braking. I'd be tempted to get new rotors. Often, turning them will only be a temporary benefit. More on that issue here; http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml

let us know what you discover

Carl

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Ok, so I checked the codes. Just the expected P0420. I cleared that last week and nothing has come back since. The engine trying to die happen again last night. Common cause was rapid braking due to an unexpected red light. Both times it was the same, I'm going about 50, and rapidly slow down, the tach drops way too low (<400rpm) right before I come to a complete stop, I slip it into neutral and the tach jumps back up to idle speeds (500-600 rpm).

The vibrations are definitely not coming from the steering wheel, I feel a lot coming from the gas peddle. They are the worst when I'm going up hill or trying to get up to speed on the interstate on-ramp and see to be more pronounced right before the (automatic) transmission shifts gears. I'm thinking bad mounts and maybe even torque converter? I haven't had the time to take it to the mechanic (or money).

My big fear is that it's a transmission problem. I had some other trany related symptoms in the past, for the last couple years there has been a slight but noticeable hesitation in shifting gears, especially when cold. Occasionally there is a slight jerk going from first to second. I'm thinking about just trading the car in while it still runs. I rechecked the milage and it's over 150K.

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Any chance it vibrates around 70 mph? I've got both symptoms and still looking for the cause.

tsii wrote:

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