Rumbling/Shaking in Drive along with odd RPM change.

[dece870717]

2011 Subaru Legacy 2.5i Premium - Some relevant info here https://legacygt.com/forums/showthread.php/can-my-old-spark-plugs-tell-me-288081.html

 

So, actually since I got the car, before even changing out the spark plugs, I noticed a strange issue mostly when I would get to work (about the only time I really drive it) and would be adjusting my car a little bit after pulling into a spot. I'd reverse a little, and then pull up slightly to be where I'm supposed to but during these adjustments I would infrequently experience a ever so slight bog/shudder in the car, like right when I'm about to just idle forward after putting it drive for the final parking adjustment, there were times it made me think that it was about half way to stalling. This issue doesn't seem to happen every single time but it got my attention after it happened the first day I took the car to work.

 

So, I recently tested out something while at home, and recorded the situation with my phone. I let the engine warm up as a now recent habit with this newer car, I watched the RPMs, and paid attention to any subsequent shuddering. The car does not seem to have any kind of vibration type issues when in Park or Neutral.

 

When putting the car in drive I notice a decrease in RPMs along with experiencing a bit of rumbling/shuddering that would sort of come and go every few seconds as I sat stationary, not severe, but noticeable. BUT, when putting it into reverse it shudders for a split second and the RPMs actually go higher and stay at a higher while in that gear. Is there supposed to be a different RPM set point for Drive and Reverse?

 

I started trying to take this issue more seriously now when just yesterday I went to the drive thru at McDonald's with A/C blaring and slowing moving up the line, then while sitting there I started to notice a little bit of shaking while moving up the stop and go line, it happened a lot more than I've experienced any other time, seemed to be not as bad when I turned the A/C off.

 

From what I've been able to gather from a little research, I'm going to first try and clean the throttle body and see if that helps.

 

Also, when I did the spark plug change out, I did use the correct NKG plugs, torqued them correctly and all that, but I did forget to make sure to see if all the plugs were gapped to what they should be, I know the plugs are stated to be at the correct gap but if they were or some are incorrectly gapped, how soon would a problem show itself for that. Also, ever since I've bought this car I've been driving it very conservatively, put maybe a little over a thousand miles total since I've had it, I'm averaging about 29.7mpg right now, and in terms of driving, I don't notice any kind of issues like hesitation or anything of the sort.

Edited June 23, 2022 by dece870717

[dece870717]

Just got it on video of it bogging down when I got to work, I noticed the lights even dim when it happens. Might need headphones or have it loud enough to hear the engine bog down. Edited June 23, 2022 by dece870717

[dgoodhue]

Honestly it seems normal to me. I bought my 2012 2.5i brand new and occasionally the rpm would slightly dip and the engine would run rough when coming to light. The was a service bulletin about it. It seem to be do it more often different parts of the year more than others (less in the summer I think because of the AC and less in the winter).

[coco26]

I don't see anything out of the ordinary in your video. The climate controls run the a/c compressor almost all the time (for a/c and heat) so its not uncommon for it to dip engine speed as its coming to an idle (coming to a stop or engaging a gear from neutral) until it can balance the load. If you feel that the vibrations are more than they should be, I'd check your motor mounts.

[dece870717]

Honestly it seems normal to me. I bought my 2012 2.5i brand new and occasionally the rpm would slightly dip and the engine would run rough when coming to light. The was a service bulletin about it. It seem to be do it more often different parts of the year more than others (less in the summer I think because of the AC and less in the winter).

I don't see anything out of the ordinary in your video. The climate controls run the a/c compressor almost all the time (for a/c and heat) so its not uncommon for it to dip engine speed as its coming to an idle (coming to a stop or engaging a gear from neutral) until it can balance the load. If you feel that the vibrations are more than they should be, I'd check your motor mounts.

This was also something I thought about a little bit. Just the fact that I don't know what right/normal is supposed to be for this car, or frankly any Subaru since I've never had one.

 

I had my previous car (2008 pontiac grand prix) for over 13 years, had it since I was 22, had about 36,000 miles when I bought it, got rid of it at around 126,000 miles. I got to know that car pretty well, if something was wrong, I could almost tell immediately.

 

Starting over sucks lol.

 

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[Plastixx]

At this point of owning my 2.5i 6mt for a little over 2 years (my first Subaru 4 banger), I think the stumbly nature of the engine is 'normal'. It's like the crudeness of the ancient SOHC engine design and modern DBW control system just don't jive well together. My '09 3.0R Outback makes the Legacy feel like an absolute turd in comparison, and I don't mean because of the power difference. Edited June 24, 2022 by Plastixx

[dgoodhue]

At this point of owning my 2.5i 6mt for a little over 2 years (my first Subaru 4 banger), I think the stumbly nature of the engine is 'normal'. It's like the crudeness of the ancient SOHC engine design and modern DBW control system just don't jive well together. My '09 3.0R Outback makes the Legacy feel like an absolute turd in comparison, and I don't mean because of the power difference.

 

I think it is Subaru trying to maintain the minimum rpm for fuel economy reasons, it sometimes dips below the threshold 25 or so rpm and it gives a rough idle for a moment.