2012 Subaru Outback 3.6R Limited is Bucking

Dec 31, 2023
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This started about 2 months ago. Sometimes while accelerating, my Outback will buck. It usually happens after the car has "warmed up" - after it has been running for at least 15 minutes. There are no lights on and all fluid levels have been topped-off and accounted for.

The week after it started, I took it to a dealership for them to have a look. They replaced the tensioner and a belt but said they couldn't find anything else. I questioned them about whether that would truly cause bucking, and the guy kind-of dodged the question by telling me what the tensioner does. So yeah, they didn't know, and it bucked on the way home from the dealership once.

Because it was still bucking, my fiancee suggested we take it to her mechanic. Her family has been taking cars to this guy for over 15 years, so we did. He drove the car around and didn't hear or feel anything, cleaned out the tailpipe, and suggested that we fill the car up with premium once to see if that helps. We did, and it did seem to help the issue for a while. We went about 2/3 days with no bucking at all, but then it bucked twice in about 3 seconds during one bit of acceleration, and it bucked harder than it had before, so we decided that this wasn't the issue. However, it has seemed to buck more often after switching back to regular unleaded.

Yesterday, we were on our way home from grocery shopping when we accelerated (very lightly) from a stop and the car bucked twice - HARD - hard enough that it felt like we had been rear-ended. We pulled over in a gas station to check under the hood, and everything looked and sounded smooth, so we shut the car off, waited five minutes, and started it again before driving home. The car did not buck again, but this bucking was so hard that it felt dangerous. Something is definitely wrong.

One thing to note is that the bucking usually happens if we're coasting for a bit and then press lightly on the accelerator. It stops if you continue to accelerate through it, but you usually have to press a little harder. Taking my foot off of the accelerator will cause the car to stop bucking, so I usually have to sort of back off the accelerator a few times to avoid the bucking.

Anyone have any ideas as to what this could be? I live in Tampa FL, if anyone has any suggestions for a good mechanic. If not, I'd be open to tips on what to tell the mechanic to check, because I don't want to just continue taking it to mechanics only for them to shrug and do nothing but charge me a few hundred dollars.

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