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Subaru bucking, sputtering, hesitating, intermittently

I own a 2004 Subaru Outback 6cyl wagon. We have intermittently experienced a “bucking” issue that is worse going uphill and/or in the rain, and usually happens at speeds over 50 mph. To a non-mechanic, it feels like the fuel supply is sputtering. We have had it to the mechanic 5 times (3 times to Subaru dealer) and, of course, the problem will not showcase itself during these visits.

Only once did the check engine light come on, and that reported a possible problem with the throttle position sensor. Our Subaru dealer has looked into that and doesn’t feel it’s the culprit. He therefore is not pushing the $600+ replacement of that sensor.

Other online threads I’ve seen suggest checking the mass air flow sensor and/or the heated O2 sensor in addition to the throttle position sensor. Since the 2 other sensors didn’t register on the car’s computer, my Subaru mechanic doesn’t feel they’re the problem.

Please help. This car is not safe to drive and we have an upcoming vacation planned.

Mr. Intermittent

Edmunds lists the following technical service bulletin for the 2004 Outback:

Bulletin number: 118006

Date: Nov 2006


Perhaps it’s time for another visit to the Subaru dealer.

Has the fuel pressure been checked? There are a lot of possible things that could be going bad, but without a check engine light on, (which you didn’t indicate you had) that narrows down the field. Fuel pressure, TCC clutch, most of the other sensors/controls would trip a CEL light if they didn’t give the computer the signal it was looking for.

Mr. Intermittent, Oh my lord. Finally someone who knows what I have been going through!!! I have been dealing with this exact same problem for over 6 months and 3 week long trips in to the dealer. I have the extended warranty so they have been doing all my work. The sputtering most of the time can be very mild to the point that I feel that my mind is playing tricks on me. But I know that I am losing power. I live in southern california and drive the freeways everyday to work. They tell me they have done everything to diagnose it. The last two times they replaced the EGR and my battery. The last time it lurched to a halt on the freeway and the check engine light came on (the first time that had happened). I had it towed to the closest dealer (which wasn’t the one who was seeing it in the past) and they claimed there was no light on and no fault in my system when they looked (but I have doubts in my mind). What fault code did you get specifically? I am about to sell the car if they can’t figure out what is wrong because I am scared to drive it everyday. Since this post have they figured out the problem?
Please please please help… I am at my wits end.

I haven’t had the problem fixed, and it hasn’t shown it’s ugly head in about 2 months, but I know it will be back.
The computer fault code was PO122 ? throttle position sensor code. After speaking to a friend of a friend’s mechanic (unfortunately long distance so he couldn’t actually help me), I learned that Subaru issued NEW TPS part #22633AA240 (~$600?) and that numerous issues were flagged to this issue, all reported as intermittent. I don’t understand why my Subaru dealer couldn’t figure this out. Next time I’m just going to tell them what to do. Hope this helps.
Mr. Intermittent.

What happened when it would begin to sputter and you gave it more gas? Mine lurches worse when I do that. It only seems to get a bit better when I let off the gas and then try again. Did they clear your computer when you took it into the mechanic? Mine did each time and it would run better for a while and then the problem would come back but it seems that the “good running time” is getting shorter and shorter with each clear.

I haven’t felt that giving it more gas has helped. It kicks back in on it’s own, usually within a second or two. I have no idea if they cleared the computer. Good luck.

I’ve had this intermittent problem on our 2003 Outback H6 for a full year, but it never threw a code until last week when the Check Engine light came- and stayed-on. My independent mechanic scanned it and also found a PO122.

He checked online in a mechanics-only forum and found nine posts on this problem. Seven of the nine were fixed by replacing the TPS. A call to a local Subaru dealer showed they had three TPSs in stock, which he considered high – unless they have replace more than what would be normal.

Long story short, the TPS was replaced this morning; only time will tell if it’s fixed for good.

One important note for the OP: It cost me $142, parts & labor, nowhere near $600. The list price for the TPS is $118, it’s available online for $85, and took less than 20 minutes to install. Anywhere close to $600 would be a complete rip-off!

THE TPS FIXED IT!!! 2004 VDC H6 58k mi. NO CEL NO CODES. Had been dealing with this problem for the last 10k and it’s been killing me, but it has been resolved. Same symptoms as above, starts out feeling like the A/C clutch cycling, then gets worse, but not all the time… 65-78 mph. Amen.