I have not experienced this in my 18

 

Can you just feel it idle, like a supercharged Hemi or is it very noticeably erratic? Something you can see on the tach?

 

It is def erratic like I would pull up to a stoplight it would idle normal then out of no where for a few seconds you could feel the idle get rough then it smooths out then it would come back and go away. The RPMS change by about 100.

 

Sounds like a vacuum hose? Check to see if everything is hooked up?

 

Everything appears to be hooked up.

 

They shimmy at idle. Normal

 

Could be lots of things but it's not normal.

 

Have you tried a fuel system cleaner? Redline makes a very good one.

 

The 392 in my 300 SRT did the same thing from just about new. It was something to do with the engine mounts. Chrysler said it was normal, and never was able to make it really go away. I learned to live with it.

My 2018 does not do this, but I’ve only got a little over a 1k miles on the clock.

 

You can feel a little bit of lope at idle but the rpm stay pretty steady. If the rpm are jumping and erratic that may be an issue.

Sent from my SM-G960U using Tapatalk

 

check what your air fuel ratio is doing. Mine was bouncing up and down and was causing a rough idle, but under acceleration it wasn't noticeable at all. If your air fuel ratio is bouncing let me know and ill send you the work order for what fixed mine.

 

My challenger hellcat has been doing this same problem forever then it threw a code for the fuel pump so i fixed that yet it never went away so took it to dodge they said it was fine im like no its not but okay so kept driving it and afr keeps bounching in drive most noticably when driving. From there i replaced spark plugs and still didnt change a thing so took it back to dodge and they said it was fine again at this point im thinking im crazy. One thing i do know is it is related to heat because a hot day will make it more prodominent. Any ideas you said you had fixed this already.

 

Depends how each individual defines rough.. however, larger displacement engines on fuel injection have very noticeable "lean run misfire" at idle which is designed for fuel mileage (basically sipping--lightest possible mixture) and is an industry wide curse for customer complaints even though it's normal.. BMW's are the most noticeable.. If the cars runs out fine then there is no issue.

 

These cars idle smoothly. Unless he has some unknown mods, there should be no roughness at idle?

 

Nobody can answer this for you. get a data log and send to a tuner or post on HP Tuners forum. It could be normal or could be 100 different things.