Forrester: hesitation and problems when accelerating

I have a ’01 Forrester (automatic) that is having some issues. When taking off from a stop, the car hesitates and chokes it way to finally going.
Sometimes, it will not go past 2,000 rpm even if the gas pedal is pressed down all the way, and then all of a sudden it will go. Periodically, there is a knock and a low idle with dimming headlights.
She is at about 60.4k miles, just had the 60k workup and a new knock sensor installed. This hesitation problem was happening before, but not as much or as bad. It is now happening all of the time. Although, the hesitation when accelerating (after getting started) can be gotten around by manually shifting through gears, but it still has issues with actually starting off.
My first thought was that it was a transmission issue, but I am now leaning towards a computer malfunction. Any ideas on what it could before I take it to the shop….
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You say 60K workup. Did that include new spark plugs/fuel filter/air filter? Did this problem just happen like you got a bad load of gas? It really sounds like a fuel delivery problem to me. Was the car serviced by a Subaru dealer or?
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The car was serviced at a Subaru dealership (Evanston, IL Subaru). The 60k workup included spark plugs and a full tune up.
The problem was intermittent at first (started off and on around 57k) and prior to the 60k service. It was better after the service but was still there and has now gotten much worse – almost to the point of being undrivable sometimes.
I thought of the bad gas thing before I took it into the dealer and ran several bottles of “Heat” and the equivalent through it, but it did not seem to do anything to fix it.
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Bill Thompson via CarKB.com wrote:

At the very least, they should have read out any trouble codes in the computer. Do you know if they did or what they were?
If they didn't, run away fast and find a shop that will.
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I don’t know what the dealer read from the computer, but the problem was off and on during that time, so it was possibly behaving while there. I still get an occasional drive now that is 100% fine, but it is rare, and the really bad choking for air feeling and lack of “go” is getting worse.
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I've been experiencing similar behavior in my '03 Forester 2.5x auto. What I'm seeing is that after a cold start and for the first 10 to 20 minutes of driving (depending on how cold the weather) starting from a stop the engine will hesitate badly, backfire and then accelerate. Also, when the engine is under load while moving, I can feel a miss and the engine surges. I checked for ECU codes but everything reads clear. A bit over a year ago I did have the dealer repair a miss on cylinder #2 (I did get a CEL that time) and they replaced the #2 plug and wire. The hesitation started about 6 months later. I was going to try some things on my own (reset ECU, manually inspect ignition components etc.) but the weather around here hasn't been the greatest for driveway auto repairs (my next house has a garage!!!). The car's only got about 18,000 miles and I always use quality fuel and have used two different gas stations, so I don't think it's "bad gas". Once the engine gets nice and hot, it runs great. My mileage is acceptable (~21 MPG average around town) but this performance issue is really driving me to distraction. Since I'm sure I'll have to leave my Forester at the dealer at least overnight I'm trying to leave that as a last resort. Any suggestions of things to look at would be greatly appreciated.
- Snuffy -
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I wish my hesitation/choking problem went away after the vehicle warmed up. Sometimes I can turn off the engine and restart and it will be gone, but other than that, it is there 90% of the time now.
Well, I’m taking my Forester into the dealer tomorrow morning. We’ll see what they say.
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Dropped the car off this morning and the dealer just called. They think it is the air/fuel ratio sensor and that the computer needs reprogamming. They quoted me $178 for the sensor and said the ECU reprogramming was covered by Subaru factory.
Given that my car has 60.4k miles on it and I didn't get the extended warranty, I'm guessing Subaru knows of a common problem (since many owners online seem to have had the same thing) and just don't want to issue a recall.
Seems to easy and cheap, but we'll see...
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If I'm not mistaken the air/fuel sensor is part of the emissions system and if so it IS covered. Check your warranty manual that came with the car.

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There was a problem with some coil packs, don't remember the year (2001?), one of the wire connectors would crack and cause arcing and a miss. If I recall, it was always the same cylinder number. ed

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Picked the car up on Friday and it seems fine now. Apparently the air/fuel ratio sensor replacement worked. I wonder if the knock sensor replacement a few hundred miles ago was necessary.
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