Rumble at idle.

[Coolmanfoo]

Curious, do your GTs rumble when idling? By rumble I mean the engine seems to rock the car back and forth. I can't help but notice my car feels extra rumbly lately but maybe I just never paid attention before.

Would a new catback have an effect on rumbling?

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[thunderstrike]

Is it a stumble, like skipping or momentary loss of fuel injection?

 

[Shifting_Gears]

My GT does this if I blip the gas at a stop. It will subtly shake the whole car as the idle settles and I freaking love it.

 

[Coolmanfoo]

Is it a stumble, like skipping or momentary loss of fuel injection?

Hard to say as I am a novice with cars. It feels like I'm on a motorcycle honestly. Smooth for a second and then a louder rumble with side to side shaking. It's noticable in the whole car.

 

[Shifting_Gears]

Hard to say as I am a novice with cars. It feels like I'm on a motorcycle honestly. Smooth for a second and then a louder rumble with side to side shaking. It's noticable in the whole car.

AC compressor kicking on? That increases load on the engine and can change idle/exhaust sound.

 

[ChromaticGrey]

Sometimes i feel it shimmy side to side for just a moment while sitting at a light. Almost like you reved it a bit and the torque of the motor shifts you.
It is subtle, last about .2 seconds and all is back to normal. Most people would never notice. If that's what you have i wouldn't worry about it.

 

[NoVaGT]

Other V8s really shake the cars from side-to-side. If you're young, you have no memory of a 1960s V8 that shook the whole vehicle side-to-side like an amusement park ride. With their ridiculous suspensions, softer than jello pudding, those cars really rocked from side-to-side along with the rumble.

Coyotes have a different firing order, and they're small-displacement V8s, so there's very little shake. In fact, Coyotes, especially the GENIIIs, are sewing machine smooth. The D.I. definitely seems to have made the engines even smoother.

Add in more isolating engine mounts, and firmer suspensions, and V8 Mustangs have only the slightest hint of the old V8 rumble/shimmy.

Hell, just go jump in a Camaro or Corvette, and feel real V8 shimmies.

 

[Zelek]

My LS1 Camaro shook more. The Mustang is much less.

 

[brucelinc]

Mine is dead smooth at idle. If not for the exhaust rumble, you wouldn't know it was running.

 

[Dfeeds]

My RPM gauge won't budge, and the car idles smooth, but I do notice a missfire on occasion. Some days it'll be worse and the engine will have a noticeable "rumble" as it missfires every couple of seconds. I've always heard these things have a buttery smooth idle so I paid attention to it, but ended up just deciding that it's probably not too unusual for a 12:1 compression engine to stumble a little bit at idle.

I wouldn't be particularly worried unless there's some serious vibration or it feels like the car is going to stall out.

Also pay attention to the weather. Excessive humidity or rain can cause a poor idle.

 

[thunderstrike]

Could be the lack of good insulation on fuel injectors and their feeder lines. Common among car brands, my 209 Jeep Wrangler does this especially at stop lights.

 

[Monopoly]

Test drove at '15 Camaro 1SS and a 10' SRT-8 Challenger they shook way more at idle. Both were manual even the shifter shakes quite a bit.

Mustang is super smooth slight shake but not much. The Borla S-Type caused a slight increase in movement but not much.

 

[Coolmanfoo]

Well after messing around more I was able to pinpoint a couple things.

First, the rumble is more noticeable if the car is in reverse with my foot on the brake. If I sit in idle it will be smooth at first but begin rocking after 10-15 seconds.

I opened the hood and noticed the engine cover was shaking around like crazy..mostly tons of smaller vibrations ( that could be normal as it's just cheap plastic).

And then there is the fact I notice a vibration at speed too. Which is also new. Usually around 70-80 I get a shake through the floor and seat.

It did just occur to me that I haven't had the oil changed in a minute. Car says it has 19% oil life left but meh that's just human entry

 

[bnightstar]

What fuel you are using ? With my regular gas the car has terrible sound. With the Shell V-Power the baby is silk smooth at idle and amazingly fast. So first start with premium fuel. Mine has all symptoms you are describing but I know it’s fuel.

 

[Coolmanfoo]

What fuel you are using ? With my regular gas the car has terrible sound. With the Shell V-Power the baby is silk smooth at idle and amazingly fast. So first start with premium fuel. Mine has all symptoms you are describing but I know it’s fuel.

I only.use 91 octane I usually go to Chevron or shell. I've never put less than 91 in the car.

What interesting is the car runs fine minus the shaking. Speed is still there. No lights no codes. Maybe I'm just being paranoid. But I feel like the shaking is new.

What I will say is the shaking seems to get worse below half a tank of gas. If I fill up then it seems to be somewhat better.

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