I have a brand spanking new 2018 Hyundai Sonata that as soon as I drove it off the lot I noticed it idles rough. Not horribly, but very noticeable. Not only do the RPM's drop a little but you can feel it.

I spoke with dealership and they said things like it could be dealership gas or something about the fact that this car was hauled from Houston and could have had extra moisture in the tank. After going through a tank of gas and still having issues I sent it to them and their mechanic even drove it for several days himself so he could see if there were any issues and he said he found no issues.

Now trust me when I say this, I'm not some kind of left brain perfectionist that complains about everything and trust me when I tell you this thing idles rough, sometimes it even feels like it's about to die but doesn't. I've had plenty of older cars that idle rough, most of the cars I've owned have been older used cars, this is one of the first new ones I've bought.

What can I possibly do to fix this issue because the dealership won't acknowledge the problem? I know how to work on cars but only when I know what to fix, I have no idea what to even look at on a brand new car and there is literally nobody on the web talking about brand new 2018 Hyundai Sonata's idling rough.

  • Welcome to Motor Vehicle Maintenance & Repair! Commented May 25, 2018 at 13:59
  • You aren't tripping or crazy. I bought a 2018 Hyundai Sonata in late November and noticed the same thing. The dealer checked it and said nothing was wrong. Yes, it idles a certain way and I think its shutting off. When I am sitting still, I can REALLY hear it running hard. Not real thrilled with that.
    – MJM
    Commented Jul 25, 2018 at 6:21
  • I have a 2018 Sonata and it idles rough also and when I'm at a stop, if you barely take your foot off the brake, then it goes back to normal, which is telling me that Hyundai has a problem with a egr valve from the motor to the brake booster. Just my thoughts, but very irritating.
    – ALEX
    Commented Oct 5, 2018 at 23:29

3 Answers 3


Agreeing with @SolarMike here, but adding to what he's saying ...

Don't fix anything ... this is something the dealership will need to fix. If you do try to, you can most likely void your warranty.

New cars in the States have an "adjustment" period. Anything you find wrong with the car during this period is subject to the dealership fixing it. Hyundai cars are no different and believe they come with 12 months worth of this coverage. Also, since it is a run-ability issue, you have greater recourse, as this is covered under the 10yr/100k mile powertrain coverage. Your warranty is in tact and you should be able to get it fixed under either of these.

If the dealership you've bought it from will not or cannot find what's wrong with it, do exactly what Mike says and take it to a different dealership. Your warranty covers it at any dealership out there.

If you still are not getting satisfaction, contact the regional Hyundai representative. Hyundai has come a long way since the mid-90's when the brand name was associated with terrible, but cheap cars. These days they are neither. I guarantee you if a regional rep is brought into the picture, things will start happening. Hyundai as a brand does not want to go back to the way it was back in the day. The regional rep has a LOT of pull with the dealerships.


Don't try and fix anything - it's under warranty and you don't want to affect that.

Your best option is to go to another dealer and explain to them (nicely) and even go for a drive with their tester so you can say when it does what you notice.


There may be nothing wrong in your car. I have a 2.5 litre naturally aspirated inline-4 engine in my 2016 Toyota RAV4 hybrid. It has occasionally idled rough when the car is charging the hybrid battery, and when I'm stopped at an intersection. The rough idle usually happens when the engine is warm; when it's cold the idle is much smoother. I think the charging of the hybrid battery requires some significant torque/power at very low RPMs. When cold, it probably isn't as aggressively charging the hybrid battery and it may operate at elevated RPMs.

I believe this happens as the size of the engine (2.5 litres) is significant for an inline-4 engine. If it was inline-6 or V-6, it probably would be much smoother.

My advice? Tell the dealership and ask them to compare your idle to another identical car. There may or may not be something wrong in your car. Be humble and be prepared to take "it's actually fine" as an answer.

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