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02 outback chug or misfire at mid-throttle

3891 Views 17 Replies 3 Participants Last post by  1 Lucky Texan
Recently purchased an '02 Outback, 160,000miles on the clock.

I've noted some "chugging", perhaps a misfire when at mid-throttle with the RPM's in the 2500 range. Tach bounces, misfire felt.

Plugs/wires/coils? Any advice on checking? Anything else I should be worrying about?

Appreciate any advice.

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if original, many items would be suspect at that age/mileage.

As for something failing as opposed to needing maintenance, I suppose the Throttle Position Sensor might be on the list of possibilities.

What is the overall condition of the car? has maintenance been done on schedule? Which engine?
It's got the 4 cylinder engine, and seems to have been well maintained. It's in quite good overall condition, I believe.

I'm guessing you haven't owned it long?

anyway, it should have had at least 2 sets, and as many as 5-6 I guess - of sparkplugs - that's one area you may need to at least inspect. And if the wires are original, they could very well be bad/weak/cracked. Typical complaints with bad wires are often in moist/wet weather or under load. OEM are best for the wires, NGK plugs are popular.

do you have a CEL on? Even if you don't, having the OBDII system scanned for pending codes might help pin down a weak sensor or problematic system somewhere on the car.
Yes, very recently purchased. Needed something affordable and (hopefully) reliable to last me 2 years or so.

No CEL on. I'll start by checking plugs and water spray test the wires. I'll check for oil on the plug boots to confirm valve cover gasket. I'll see if I can get my hands on an OBDII reader.

OK, sounds like you have done some reading or have had experience with soobs in the past.

While you're under the hood, wouldn't hurt to at least clean, maybe replace the PCV valve. Inspect the battery cables, maybe refresh.tighten any ground connections you find, inspect vacuum/vapor hoses, hose out the bugs from the radiator fins, inspect the accessory belts, inspect all fluids, replace any that are darker than normal, smelly or suspicious. make sure the tabs are seated at the bottom of the air filter 'box'. If you mess with the coolant, read up on 'burping' the system when refilling. new thermostat should be OEM or 'maybe' Stant Xacstat. best to test them in a pot on the stove before install. they should open at 170*. New radiator cap might be a good idea. Inspect the axle boots - particularly the inner ones, for splits/leaking grease.

You might look for a cabin air filter. Behind the glove box. Could be dirty if equipped. ( will have instructions)

brake fluid is hygroscopic - might need flushing/bleeding if old.

make sure all 4 tires are the same model and same amount of wear. Many folks like to inflate them 10% or so above the recommended pressure.

I bet some other folks will have some tips for you. good luck with your new car!
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Thanks, 1 Lucky Texan.

This is my first Subi, but I'm not a stranger to older vehicles... And I did a good read-about before posting. Much of what you suggest I checked prior to purchase (especially things like boot leaks and the like, been there, done that!). The engine/tranny seems to show only typical very minor fluid staining, just normal years worth of normality.

The chugging/missing is very remeniscent of similar issues I've had in the past, where either old plug wires or leaking valve cover gaskets were the culprit. I've entered into this purchase with eyes opened as much as I could, knowing that a 10 year old car will not be completely issue free. Just so long as I can keep it going and passing inspection on an annual basis for 2-3 years, and I'll be quite content.

Fingers crossed for old wires,

if you haven't tried it, you might consider some Techron or maybe seafoam - could help clean out any injectors that are dirty.

The forum is a great resource and, if your car ends up having a 'hard' problem, someone here will be able to help I'm sure.

let us know what fixes the misfire.
I'll be sure to letcha know how it turns out...

A can of Seafoam sits on the bench in the basement. I'll give it a splash.

Well, here's what I've done so far....

Picked up OBDII reader (Canadian Tire had'em on sale) and scanned. No codes, none pending.

Checked what I have for service records, and the plugs and wires were done about 60,000m ago. Found a service record from '09 with similar stated symptoms with CEL, and front O2 was replaced. Timing belt done about 50,000m ago. All significant maint. (beyond tires and oil) done by local Subi dealer, it seems. I don't have complete records, but maybe they do.... I'll look into it.

Pulled plug boots, no oil on any, no signs of tracking, white silicone grease visible. Pulled coil ends of wires, no corrosion, silicone grease visible.

Haven't spray tested yet, not dark yet and wifey just took the car for a girls thing. I'll update again when I try next...

Unless spray test turns something up, I guess I wait for it to throw a code? Misfire is very intermittent, often only one incident (hill comes, ease in gas, chugga, more gas, off we go!) in 15mi drive.

I'll add some seafoam once I've burnt the tank down some.... She's full right now.

Appreciate the suggestions so far!

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what brand plugs and wires were used?

these engines aren't overly forgiving of cheap stuff. i've seen new out of the box wires cause misfires. usually the cheap ones which you probably don't have but worth a check.
Haven't had the plugs out yet, but the wires are Bosch.

An interesting possibility. Anything I can do to rule this possibility out beyond ye olde water spray?

others here have complained of Bosch wires.

also, unless the plugs are platinum or iridium, they are likely past their prime at 60K.
Well, did the water spray at twilight tonight. Used garden hose with nozzle on fine spray. Didn't note any misfires or arcing.

scanned for codes again, still none found current or pending.

All fluids check out OK.

I'll add the seafoam in a couple days when at about half tank, and then wait'n'see for a bit. Either things clean up, it throws out a code, or..... LOL, we'll see, and I'll post back. I may break down and just bang some plugs and wires in.

Sure do appreciate your input, guys,

Another non-Subaru forum suggested some possibility of xmission difficulties masquarading as engine misfire/stumbles.... Is this likely? How might I rule this out?

I'll resummarize here, and try to be as clear as possible:

2002 4 cyl auto.

Generally occurs during a gentle to moderate hill climb when a little throttle is eased in for climb, at somewhere near 30-35mph.

I drive along, reasonably level street, and a hill is approached. RPM's are at about 1500 on approach, doing 30-35mph. I feed in gas to maintain speed up the hill. TC unlocks, then tranny shifts, 2500rpm give or take. Hesitation is felt, usually at about 2500rpm, and occasionally the tach can be seen to twitch slightly a time or two (dropping 200rpm or so), or engine may just seem to bog/fail to deliver power. As more throttle is fed in, the engine seems to recover, the tranny shifts again, now in the 3K range, and off we go. Around 3200, the engine seems to come "on cam".

Haven't been able to reproduce it reliably otherwise. No miss noted in neutral. Seems to require some load.

I'm loosing sleep.

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Well, a week on now, and I've had Seafoam added to the half-tank remaining for 2 days. The vehicle seems to be behaving much better now. The problem may be solved.

FWIW, the plugs are NGK platinums.

Well, the problem's finally been identified and corrected, so I figured I'd post the solution here so others may benefit.

I disconnected the battery for the weekend 2 weeks back to see if that had any effect on the symptoms, and lo and behold, it did. The car's performance improved for a time, slowly deteriorating again, thus pointing firmly at an EFI related problem. Disconnecting the battery basically set the computer to defaults, and then it slowly "learns" based on sensor inputs.

Armed with this info, I brought the car in to the local Subaru dealership, and told'em have at it. They insisted on dropping the manifolds to check the exhaust valve guides (their leading suspect, as they were resistant to the idea that there could be a sensor problem without a light or code). All was found mechanically fine.

Hooking the car up to their diagnostics computer, they eventually determined that the front O2 sensor was giving erroneous data, leading the computer to tweak the mixtures lean. Simply replacing the O2 sensor has got the car performing normally, much to my relief.

Slightly annoyed with Subaru's insistance on checking for a problem I ruled out (the exhaust valve guides), but that is tempered by knowing that the engine is mechanically in decent health.

Ultimately, the ordeal set me back about $500. So, all told, I've got about 3500 into this car (including purchase), so with luck I've got a decent thing going now.

It is nice when power output corresponds with throttle position.

Thanks for your input, fellows.

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thanx for getting back to us!
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