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2019 Elantra Limited Shudders periodically when idling

My 2019 Elantra Limited will do a shudder that you can feel in your seat while idling. It’s only 2 months old, it’s been doing it for a little over a month and wanted to see if anyone had ideas or experienced this and it’s “normal.”

The car has to have warmed up first for about 5-10 mins. It started a month ago at a stop light, it felt like someone very gently bumped into my car because I felt a shudder, and it felt like it was coming from the back, because the back/base of my seat is where I could feel the shudder most. I literally checked once to see if someone had gently bumped into me. They hadn’t.

Then while idling in a parking lot playing a game (Pokemon Go), the car would suddenly shudder intermittently. A couple times it was a VERY strong shudder, but it doesn’t do that much now, it does a shudder that feels like when you shut the engine off when it’s “still in a cycle” or for whatever reason it shudders sometimes when you turn the engine off.

Took it to dealership, waited, mechanic came out to feel it, I said it might take awhile, and it did do it once after about 5 mins, but he wasn’t paying attention and didn’t feel it. So without being able to show them it on demand they can’t do anything or pay attention enough to notice.

Been watching the RPM, after warmed up (5-10 mins) it idles a little below 750. But then it’ll do a very small dip, then recover, it can bobble up and down a few times and nothing happens, but then it’ll do a bigger dip of probably about 100-200 RPM, and THAT’S when the car shudders and then the RPMs recover to their normal position.

I played around to try to get this to be repeatable, and if I use something that draws electricity I can force it to drop RPMs while idling and shudder. AC is off. Have HVAC on auto usually, but if I’m idling and crank the fan speed, the RPMs dip 100 or so, the car shudders and then recovers back to normal idle RPMs. Sometimes it won’t do it immediately, so I just turn the fan up, turn it down, turn it up, and the RPMs start fluctuating and after doing it about 3 times, RPMs do the larger drop and car shudders.

If I’m at a stop for a bit, when I take my foot off the brake, the RPMs also drop ~75-100 and the car shudders. This is less noticeable since usually you hit the accelerator quickly, and pressing the gas seems to cut the shudder short.

All the shudders are quick, image a human shuddering from chills. That’s basically what the car does. But it does it so frequently while idling it’s worrisome.

Anyone experienced this, or have any ideas?

Rather than an idea, I have one word of recommendation:
WARRANTY

It doesn’t matter whether one person–or many people–have experienced this problem with their new Hyundai. This is a warranty issue, which requires free diagnosis and repairs for you. If the dealership is unable or reluctant to do the right thing, then you need to contact Hyundai at the corporate level. Contact info can be found in your Owner’s Manual

The only time I’ve had the sensation where it felt like someone bumped me in the rear while stopped, and you look in the mirror and there’s nobody there is, when transmission started acting up.

Tester

The cycling on and off of the air conditioning compressor can produce this symptom.

Warranty - yes! A save your documentation in case you decide to appeal to Hyundai above the dealer level. Good luck and please keep us informed.

I get it’s under warranty, but warranty claims are INSANELY difficult to get them to acknowledge. They will lie and say EVERYTHING is normal even if you concretely prove it is not. Currently going through that with something else about the car that’s visual, and Hyundai Consumer Affairs (corporate) even made up this ridiculous lie that makes absolutely no sense. Even the guy on the phone couldn’t justify it and said, “I don’t know, I’m not an engineer, here, talk to the BBB auto resolution” and this week they’re forced to provide a solution or we go to adjudication.

The people who are “mechanics” at the dealership don’t really care much, so I was looking for some idea of where to steer them… if anyone has noticed this or has an idea of what could cause this? Why when it’s idling and you use something that draws power does it dip in RPMs and shudder? Should a car ever dip in RPMs and shudder? I did take this to the dealership already, and since the mechanic who sat in the car “didn’t feel it,” I only had a few minutes, and it won’t do it until the car is warmed up, they said, “your car is functioning normally.”

Get a voltmeter that plugs into the 12V power socket (formerly cigarette lighter).
This will tell more about what’s going on.
Example:

https://www.amazon.com/dp/B0773BYS6P

Thanks, I just booked an appt with the dealership (again) for tomorrow and will ask them about this. Do you think that it could have something to do with power, and what exactly would the voltmeter show that’s right or wrong? I just like to know in case, you know… they don’t. Also, the easiest way to force the shudder is to just turn the fan (no AC, it’s 50 degrees here) in the cabin up and down, it literally makes the RPMs go up and down, I made a video of it just now.

https://drive.google.com/open?id=14OmeXy7xTQPPLIx6qFjaNCP-Q7jxRqTr

You can see how much the RPMs drop JUST from turning a fan to a higher and lower speed. I wasn’t really even watching the RPMs while recording, I just said, “It shuddered,” each time it did, and watching it back, it coincides exactly with each time the RPMs dropped. I’m going out on a limb that a fan drawing some electricity shouldn’t cause the engine to shake and the RPMs to drop that far. It’ll do this by itself, over and over, but rather than sit and wait for it, I can just force it to happen this way. Same shudder. Sometimes it’s stronger than other times.

Sounds like Hyundai’s Alternator Management System (AMS) hasn’t been perfected. The AMS sets the charging rate depending on conditions to save fuel. There is probably a very low charging rate at idle and toggling electrical loads induces a problem. Your dealer’s service department may not be able to improve this without an engineering change to the AMS or Powertrain control module.

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Would it make sense in that scenario for about the first month of owning the car it didn’t do this (car is 2 months old)? And that it does it randomly by itself when it’s just sitting there idling? It does the exact same behavior when it’s about to shudder, the RPMs start bobbling like in the video, and then suddenly just drop. And I’m literally just sitting in the car and it’s idling without anything being touched. It also drops the RPMs when you take your foot off the brake at a red light, but only if you’ve been stopped for a bit, which worries me. Also, it won’t do any of this when the car is still cold and hasn’t warmed up, it keeps the RPMs solidly around 900-1000 and they do not fluctuate at all… until the car is warmed up and the idle RPMs decrease.

I’d be inclined to monitor the battery voltage and charging current from alternator to battery as this was occurring if it was my car. Might provide a clue to what’s happening, especially if compared to another new car on the lot of similar configuration. Besides the hvac blower motor, see if turning the headlights on bright, turning seat warmers on, turning rear window defroster on has any effect. Those are also big current draws. One theory for why you didn’t notice for 3 months is the battery was new then, so it held its charge better than it does now, which puts more demand on the charging system now than before.

It’s possible there’s some sort of engine problem too. Turning on electrical stuff puts a bigger mechanical load on the engine due to the alternator needing to work harder. Mechanical loading the engine will often show up subtle engine problems. The other way to put a mechanical load on the engine is to accelerate when going uphill. If you feel some shuddering or missing or hear some pinging then, that would be an important clue.

Another idea, ask to take a test ride in another Elantra on the lot. It is possible the symptom hasn’t changed, you’ve just become more sensitive to it. Years ago I had a VW Rabbit, had been drivng it for a number of years, when one day I did some diy’er repairs to the fuel system. Testing the repairs out on a test drive I noticed a high pitched whining noise I’d never heard before , happened during rapid accelerations. Trying to figure this out too quite a bit of time, but eventually the result was that noise had always been there, I’d just never noticed it. So somethings like that has to be considered.

The fallback position is to let the dealership keep the car and have one of their shop techs drive it as their personal car for a week. It’s almost certainly going to happen to them, so when it occurs the shop tech will have a better chance figuring it out. Best of luck.

The car will be 2 months old tomorrow. It didn’t do anything wrong for the first month (Bought Nov 15). Then the shudders started. If I put all the windows down at the same time, I can get the RPMs to drop like in the video, but the car didn’t shudder when I did that. I do have the heated seats on pretty much all the time, but on the lowest setting, and the HVAC on auto, so it gently blows, and all my lights (including headlight) are LEDs so they’re pretty low energy, and it’ll still shudder randomly when it’s idling. I just had a hunch a week ago, that’s why I messed with turning the fan up to max quickly, and sure enough, it shuddered. So that’s a way I can force it to shudder, but it’ll shudder by itself too. I needed a way to force it to shudder so the mechanic doesn’t have to sit with me for 10 minutes in the car waiting for it to do it.

I’ve tried driving up a mesa, and it performed fine. I did it on purpose to see if anything would happen. It won’t shudder when the engine is active, and works great when it’s moving. It’s only when it’s idling that it gets obnoxious. This time at the dealership I can get it to shudder, no problem with turning the fan up and down. I’ll ask them to check the battery, but my car has BlueLink and it says the battery is at 90% right now and there are Elantras that draw more energy than mine, so I can’t imagine the battery going bad after 1 month.

I’m the weird type of person that notices every single thing. I’ve driven other Elantras before and they do not do this shudder. I actually test drove a couple different ones for 3 hours last year (deciding which to buy), no shudder.

Another idea, the idle rpm management gadgetry isn’t working properly. I’m not familiar w/that car’s design but I expect it uses a drive by wire system for the throttle. What that means is there’s no direct mechanical connection between the throttle pedal and the throttle valve in the throttle body the engine uses to change rpm. Instead when you press on the gas pedal a computer reads how much you’ve pressed, and programs a little electrical motor in the engine to move the actual throttle valve accordingly. That system is also used to make small changes to the idle rpm to prevent stalling, like when you turn the headlights one, or turn the AC on, things which impose an extra engine load temporarily. The way it works on my Corolla (which has a mechanical linkage to the throttle valve) is it opens another valve to allow more air into the engine (separate from the throttle valve) via solenoid action when I turn the headlights on to prevent stalling. During warmup on the other hand there’s a separate valve which also allows more airflow into the engine due to coolant temperature changes. But on your car all those functions are probably incorporated into the throttle body electrical motor and its programming. A problem with the pedal position sensor or the electrical throttle motor or the coolant temperature sensing function for example could cause this. As could a transmission glitch, presuming you have an automatic.

Yep, it’s an automatic. The only time I’ve ever used the AC was in the first month I got it before I had it tinted. And that was when it never shuddered. Didn’t shudder when the AC turned on automatically to maintain the temp, didn’t shudder when the AC turned off. Wouldn’t have known the AC was on except for the fact that the air blowing out was pretty cold and then I noticed the AC button was lit. I tried turning on the AC myself when I was messing with the fan, and that didn’t make the RPMs drop nor make it shudder The fan going faster and slower REALLY does it, I don’t know why. Hopefully they can figure something out tomorrow… getting them to even notice something is like splitting a photon, that’s why I recorded the video, I needed VISUAL proof that the car is DOING something that looks wacky and they should pay attention to what I’m saying and to what’s happening. That’s why I asked you guys too, so at least I have a little more knowledge, because I’ve googled my life away the past 3 weeks, and just want any ideas I can float by them.

The way it shudders though, the cadence and the erratic-ness of the shudder is odd. I described it like the engine turning off, which is true, it’s a shake you can feel like that, but the way it shudders is jolting and faster; it’s not a fluid shake, when you turn the engine off and it shudders, that feels smooth. This feels like something just happened that wasn’t supposed to happen.