99 Forester L, manual, 65K

 

There are really three symptoms here that may or may not be related:

 

1. When the car starts, the RPMs stay high for a while before calming down, rising and falling btw ~1100 and 1600 for at least a couple of minutes before descending below 1000. If I step on the gas, they quickly settle down to ~1000, pause there for 5 or 10 sec, and then drop to typical idle range.

 

2. Idle speed seems a bit low: tach reads ~600 (though I understand this may be lower than the actual RPMs).

 

3. Idling has a smooth "background," but is punctuated every 2-3 seconds by rougher vibrations, enough to rock the car slightly. What I see under the hood: the engine is jerking about a horizontal axis running from its front to its rear.

 

Context: I recently had a bad front crankshaft oil seal replaced at the dealer here in Oakland. While they were in there, I had the oil pump resealed and the cam belts and timing belt replaced. I don't remember noticing the rough idle before the timing belt job, but I hadn't owned the car for long at that point (weeks), and I can't be sure the idle problem cropped up then. Can't remember if the idle speed was different beforehand, either. The revving on startup DID occur before I had this work done on the car.

 

In an attempt to improve the idle, I replaced the fuel filter, PCV valve, and spark plugs & wires (latter three were all original by the looks of it). The revving on startup has improved a bit, but the idle is the same.

 

I have driven other Subarus with boxers, and the idle was not this rough. Are there other things I should check/replace, like the O2 sensor? Should I suspect a sloppy timing belt job? Any help would be appreciated.

Things I'd look into are if you haven't had them done, clean injectors &/or have a motor vac or something similar to help clean out carbon gunk in the engine.

 

Next I'd look at the IAC valve, and possibly a failing O2 sensor.

Since your crankshaft oil seal was leaking, It may be possible that some oil got onto the cam/crank angle sensors and fowled them up...sounds similiar to when mine went south Any check engine light?

 

Good luck,

Kevin

My 97 Legacy has EXACTLY the same behavior when below operating temp.

When I park after coming back from a trip, the car idles at around 600-650.

I really thing this is quite normal but I could be wrong.

The warmup description you give sounds normal to me except for the misfire part. You may be able to look at your trouble codes and see if there is anything stored in the ECU like, which cylinder is misfiring.

 

If you have no codes for a clue as to the location, you may be able to track the problem down by removing the injector wiring, one cylinder at a time, to see if that will give you a clue as to which cylinder is having the problem. I think you have sequential injection so you can do this. You could also remove one plugwire at a time to help find it.

 

Hopefully it is carbon buildup, like Josh said, and using a fuel cleaner may help eliminate the problem.

 

Glen

No check engine light, and no codes in the ECU. I'm having the injectors cleaned & will check out the IAC too.

 

BTW, is there a site, or a thread somewhere on this board, that has a list of error codes & procedures for accessing the ECU, retrieving codes & clearing?

 

Will report back.

 

*** [time passes] ***

 

After having the injectors cleaned with one of those 3M setups, the background idle was smoother, and acceleration had improved, but the "hiccups" in the idle that shake the car were still there. The revving at startup has now calmed down to a normal warmup routine.

 

I also removed and cleaned the IAC valve, which was a little gunky but not too bad. No noticeable difference after doing this. Maybe I'm being too picky, and this is just how the engine is going to idle.

 

Glen, is there no way that disconnecting plug or injector wires one at a time could damage the engine?

 

Taylor

No,

 

But pulling one spark wire kills 2 cyls at a time due to how it's wired. You'd almost want a "dummy plug", grounded to the car, to move that wire to in order to let th other cyl fire.

 

Meep

Geo, I have the exact same "hiccups" at idle after I changed spark plugs and air filters this weekend. did you ever find the cause?

The IAC valve is what you are after. There should be a little (in my car grey) sensor (its magnetic) on the top of it. You can loosen the screws and turn it. In my '92 Legacy, I turned it clock wise quite a good bit before the idle smoothed out. I idled it down to what the book told me and its been running smoothe ever since. Also, you may want to replace the PVC valve and your TPS. It worked for me! The adjustment on the IAC tweak made all the difference in the world and the PVC valve needed to be replaced anyways.

I did not see TPI or TPS mentioned. Throttle Position Indecator or Sensor. Test it & tell us.

 

Karl

The TPI (TPS) shouldnt matter much, since his car isnt reving up alot. None of his symptons matched that of a "stuck" TPS.