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1999 Subaru Forester rough engine idle


I’m thinking about buying a used Subaru Forester with 150k miles. The up side is that the used car lot wants $2000 for it. The down side is that it idles roughly. With the hood up, you can see the engine shimmying from side to side. Also, the check engine light is on. If you step on the gas to bring up the RPMs, the engine smoothes out right away, but I think there’s still a hint of roughness around 2000 to 3000 RPM. We’ve heard two opinions as to what could be the problem. The used car folks took it to their mechanic, who thinks it could just be carbon build up. The computer said something to the effect of poor power from cylinder #4. Someone else took it to the local Subaru dealer, who said that the car needs a new engine due to a head problem. So, the questions are:

1) What else could be the cause of the rough idling?

2) Would you take the chance and buy the car?



The engine may be on the way out due to low compression. Even one cylinder down can cause a rough idle/smooth at elevated RPMs situation.

These cars have mechanical valve lifters that SHOULD be inspected every 30k miles. However, only one car in a million ever gets this service performed and a tight valve can cause valve and cylinder head damage. Most owners luck out by not having this service performed; the unlucky minority wind up with expensive engine issues.

A compression test could be run to verify any mechanical fault but my gut feeling is that this car has a serious issue due to lack of valve lash inspections and the Subaru dealer is quite likely correct.

1-who cares
Never buy a used car with something obviously wrong with it. If the person that owned it wasn’t willing to fix something you can easily observe, he hasn’t been spending money maintaining the car either.


Normally, Subaru engines have a far steadier idle than other 4-cylinder engines. At the very least, this car has suffered from poor maintenance, and in the extreme it may have some serious mechanical issues, as suggested by ok4450.

Surely there have to be some used cars in your neck of the woods that are not so obviously flawed.
Why would you even consider buying a used car in this condition?

There are a lot of things that could cause the rough idle. If you decide to purchase this car be prepared to have the headgaskets replaced on it and spend more on repairs than for the car itself. Those engines were fairly prone to have headgasket troubles.

So it has a CEL and they have not bothered to find out what the CEL code was? I’d bet they know why that CEL is on and are not going to tell you. If it was going to be easy to fix, they would have done that. I would run from it.