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OldSubaru1

91 Subaru Legacy wagon shakes at start up and while idling, also has acceleration issues. Mechanic said it is fine?

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I purchased the car used about 6 months ago and had $2,500 worth of work done on it to get it through inspection. It seemed fine after that other than the shaking issue, but a few months later I also began to have acceleration issues. I had an oil change done in October at which time I also paid $50 for a diagnostic test and was told that I needed a new battery. But other than that I was not told that there is anything wrong with the car. I assume that the mechanic probably thought that my issues were linked to needing a new battery, and I honestly thought the same. However I basically continue to have the same issues even with a new battery. That being said, does anyone have any idea why the car may be shaking while idling, for instance while stopped at a traffic light, or why it may have trouble accelerating, and/or should I even bother to have it diagnosed again? Note that the car does have about 177,000 miles on it.

If any more information is needed let me know.

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177,000 is nothing for these cars. Our last wagon was sold still running like a champ at 350k+.

 

When was the last time your spark plugs and wires were changed? These motors are hard on them - especially if they are anything besides subaru or NGK brand.

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177,000 is nothing for these cars. Our last wagon was sold still running like a champ at 350k+.

 

When was the last time your spark plugs and wires were changed? These motors are hard on them - especially if they are anything besides subaru or NGK brand.

agree, spark plugs, and perhaps plug wires. At least pull a spark plug wire, and see how much it is worn. Easy do it yourself project to change yourself.

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I'm not sure about the spark plugs/plug wires. Do these have to be in good shape in order for the vehicle to pass inspection, and also how long do they typically last (in this type of vehicle) before needing to be changed or replaced? The reason I ask is because I just took it through Maryland state inspection when I purchased it in June, and I had $2,500 worth of work done on it at that time. If the plugs are required to be in good shape, then they must have been in good shape at that time when it passed inspection. But again I am not sure if this would have been a requirement. I will have someone take a look at them, but I am just trying to get an idea of where things should stand for the time being.

I don't recall being told anything about the spark plugs being or needing to be replaced when I took it in to get the initial work done. I also looked at the paperwork, and I don't see anything about it on there either.

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Just change the plugs and wires. Super easy to do on these cars cheap and is more than likely the problem

 

Use good quality wires and you shouldn't have to worry about them for a long time.

I like beldin max life wires (Napa lifetime wires)

Edited by mikaleda

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Spark plug wires can "look" fine, but not be functioning properly. - and they do "age"

Spark plugs wear out over time as well.

 

get basic, NGK copper core spark plugs for your year/model , and a set of NGK spark plug wires for your year/model.

It is a pretty easy job to change yourself with basic tools.

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I am going for a long shot, but if nothing seems to work try swapping out the injector circuit resistor on the passenger side strut with the ceramic insulator in an aluminum case. This was a cure for a 91 legacy ls way back in the day even after an engine swap and an injector swap before discovering this. Any replacement part would be easiest from a salvage car.

 

Subarus are sensitive to their plug wires, so take this advise once the wires and plugs have been ruled out. 

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I just did plugs, wires, and coil on mine, which showed the same acceleration issue and it is now fixed. Used all Subaru parts per advice on this forum. Do plugs and wires first and see how that goes before doing the coil as mine was $225.00. Good luck.

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The dead giveaway for plug wires is if the acceleration issues and all are worse on rainy/humid days than clear sunny ones.

 

Also the issues tend to show as the engine will sputter but then clear up above 3000 rpm

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It also could be a vacuum leak.  With the engine running check under the hood and see if you hear a strong hissing sound around any of the rubber hoses.  You can also take a can of carberator cleaner like Chemtool and lightly spray the length of the vacuum hoses one at a time while the car is running.  If the car stumbles or the idle changes while you ar spraying you have found your vacuum leak. 

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It also could be a vacuum leak. With the engine running check under the hood and see if you hear a strong hissing sound around any of the rubber hoses. You can also take a can of carberator cleaner like Chemtool and lightly spray the length of the vacuum hoses one at a time while the car is running. If the car stumbles or the idle changes while you ar spraying you have found your vacuum leak.

That's a good point.

I just thought I would add this though.

 

Do this test on a cold engine only. It could cause a fire on a wa engine

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I have heard of people using an unlit propane torch to search for vacuum leak, instead of spraying carb cleaner all over.

Just 'spray' the propane on the suspect area, and it should react the same as if you sprayed carb cleaner.

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