2011 GT - idle vibrations and thump noises?

[FIVE-OH]

Hey guys, I have a 2011 5.0, auto, 18,000 miles, tune, axle back. Ever since I've owned it (and when it was stock too) I have noticed the idle is kinda crappy, warm and cold. Worse with a/c off, better with a/c on. Basically what I notice is a slight vibration every 20 seconds or so if you sitting in it, and if you are outside it you can hear a slight thump sound every 20 seconds or so. Idle rpm itself is pretty steady on my logs, tuner said logs all look good.

I did some research and it seems this is normal according to some forums? Do any of you have the same thing, and if so what is causing it? These 5.0's sure don't idle as smooth as my old 4.6's did...

Thanks.

 

[jumbowolfe]

Mine's not tuned, but mine idle's as smooth as glass. I do get some vibrations at start up, but I think thats some metal around the stock headers rattling. I have an auto as well.

I'm at 48k miles on my 2012 (bought it with alot of miles) and it is rock solid on the idle. You might find someone locally to check the tune and see if something is set wrong?

 

[Sky Render]

It's normal. The fuel trim goes a little wonky every few seconds to keep the catalytic converters from overheating or getting too cool.

 

[claudermilk]

Seems normal to me. '13 with 29k on it, completely stock and it's always done that. It seems like a little intermittent misfire at idle.

 

[FIVE-OH]

It's normal. The fuel trim goes a little wonky every few seconds to keep the catalytic converters from overheating or getting too cool.

That would make sense. Just odd that it is so obvious on these 5.0's.

 

[black2008gt]

Happens to mine all the time..Kinda feels like someone is bumping the back of the car. Its perfectly normal just enjoy the car.

 

[V8 Vol]

funny you bring this up because I was wondering the same thing. I figured it was something in the tune.

I didnt have it stock long enough to find out if it did it then or not.

 

[FIVE-OH]

I didnt have it stock long enough to find out if it did it then or not.

I'm sure it did. The only thing that makes it do it less is having the compressor on...from what I am starting to gather it is perfectly normal for these engines.

 

[BAKnBLK2010]

I've had two of these cars (2011&2012) and both of them have had the misfire at idle with the stock tune or aftermarket tune.

 

[BadHabit2Break]

Mine does it also.

 

[RocketcarX]

My 4.6 has always done that, shakes a little like it has a super mild cam. It's never been a problem.

 

[TimMcc]

Mine does it as well.

 

[Sky Render]

So I set my Aeroforce gauge up to monitor wideband air/fuel and watched it whilst sitting at a stoplight.

Every time there was a "bump," there was a spike in the AF ratio. That means the computer is leaning out the mixture a tad to increase EGT and keep the cats warm.

 

[FIVE-OH]

So I set my Aeroforce gauge up to monitor wideband air/fuel and watched it whilst sitting at a stoplight.

Every time there was a "bump," there was a spike in the AF ratio. That means the computer is leaning out the mixture a tad to increase EGT and keep the cats warm.

Cool, good to hear this is normal and there for a reason.