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Discussion Starter #1
Hey guys,

New owner of a 2015 GT manual transmission. I purchased mine June 21, 2015. Very happy with it and I have been driving it ever since I took it home. Yesterday morning, I started the engine as usual and immediately I felt a change in its idle characteristics. I can also feel the car shake side to side every 5 seconds or so and the exhaust note seem to have an additional "domp" or "womp" sound to it when this shaking occurs.

I pop the hood open and I can see the plastic engine cover vibrating but the actual engine itself not too much but I can still see it.

So I went back to my dealer yesterday. To my disappointment they blew me off and said if it's not throwing any CEL they can't do anything really.

I'm stomped. Is this even normal for a V8 engine after more than a week of use?
 

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Have them monitor your engine for misfires while it's running.


Only the rocks last forever.
 

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Discussion Starter #3
By the way, it runs fantastic. When accelerating it is very smooth. Just on idle I can feel the car swaying side to side and the recaro seats I can see somehow getting the vibration too.
 

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Discussion Starter #5
Does the AC being on/off change anything?


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Good question. It seems like the vibration goes away a little bit when the AC is on.

When I let it idle for a long time like 5 minutes or so, the vibration is much worst like the engine is going to die but it still continues to run.

I just scheduled an appointment tomorrow at my dealer. They blew me off when I went there yesterday maybe because there are customers in line but I just can't accept the fact that they wouldn't even spend 5 minutes to see what was going on.
 

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I had the same issue in my '14 and took it to my dealer who stated it was a product of "normal A/C condenser operation." I got the same response from another dealer when I went out of town for a second opinion. I can feel it in my '15 too, but it's rather tame compared to the '14.


5.OH
 

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Discussion Starter #8
I had the same issue in my '14 and took it to my dealer who stated it was a product of "normal A/C condenser operation." I got the same response from another dealer when I went out of town for a second opinion. I can feel it in my '15 too, but it's rather tame compared to the '14.


5.OH
So do you feel that shake at idle too? Mine is like a cyclic interval and i can feel the car sway from side to side plus i can see the engine cover really vibrate. So weird. It's not throwing any codes either. It was so smooth on the first week then idle issues. Car runs fine.

I'm wondering if an idle relearn procedure would eliminate this issue.

Does anyone know if the idle relearn procedure for the 2015 is the same as the previous years?
 

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87 is fine unless you have a custom tune



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2015 GT Premium Triple Yellow
Niche Essen Staggered
JLT with tune
Borla ATAk cat back
 

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I have noticed it too op and i use 93 octane on mine. Are we suppose to be us 87? I read the manual and i am fairly certain it was saying 91 or above gas or i might have misread it as i spent 2 hrs reading about all different things.
 

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I have noticed it too op and i use 93 octane on mine. Are we suppose to be us 87? I read the manual and i am fairly certain it was saying 91 or above gas or i might have misread it as i spent 2 hrs reading about all different things.
Delear said they couldn't find anything wrong. I used to fill her up 87 but now I'm sticking to 93 because the vibration and shaking toned down significantly most especially after revving the engine.

I also saw a YouTube video where this guy is reviewing the '15 Mustang and on the engine bay part I can see the same symptoms of the engine. I guess this is normal.
 

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Our 2015 GT only has 2,100 miles on it, but there is a huge difference between how the engine idles with 87 octane in it and 93.
87 octane lopes a little bit and you can feel it in the entire structure of the car. 93 octane, the idle is almost as smooth as silk. I also get about 4 mpg better on 93....even the sound of the exhaust system is different between the two octane levels, with the higher octane sounding MUCH better.
I wonder how far the engine retards the timing to avoid detonation when the octane level is so much lower?
 

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Just stick to 93, and good gas stations. For example I was putting 93 on Arco Ampm gas realized it wouldn't last. I recently put 93 on chevron and OMG I do not bs my car rides better and last much longer. These new mustang engines deserve the best now my 96 I could careless I put cheap gas haha.


-1996 GT, 2015
 

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91 octane or higher is by ford the reccomended fuel of use.

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