Cruise will NOT maintain set speeds. Driving on the same roads now as I did with a 2014 Sonata and the control will NOT maintain set speed, car slows down about 3 or 4 MPH and then throttles up like a race car to restore speed and then over shoots set point. If you go down a slight grade, the cruise tries to hold the car back by down shifting and the RPM goes very high and the down shift is a shock. When you go over the top of a grade, the system RPM drops down and the suddenly engages and it feels like it shifted gears.

I am unable to drive the car in the ECO setting because of the fluctuations, while in the other two modes there is less hunting. I am visiting my dealer on Monday to have a Tech ride with me to investigate problem Per the service manager, "sounds like all normal operation to me" - we will see. Very disappointed in the 2018 performance so far. LESS than a 1000 miles

Will keep you posted.

Update from Oct 14, 2018: Bad news -"that is the way the system works". So I will have to change my driving habits and learn to use the 2018 system the way it is. The system is OVER DESIGNED and when you go down a hill the system down shifts the RPM's go through the roof. I can assure you if I had the opportunity to drive this car and tested the Cruise Control and it behaved like it does, I would have CANCELLED the sale. Very, very disappointed in this feature. Living in PA and having hills to go up and down this system really disappoints. The 2014 system had it all over this latest version. Be aware consumers. NO CHANGE NOW OR ANY COMING IN THE FUTURE

Purchased a new Hyundai SEL 2018 just after Christmas 2017. Drove it home. Didn't use the cruise control at the dealer or on the way home. Couple of days later took the car out. We have very strict speed zones going and coming from our home. I use cruise control exclusively to traverse the area. As always, I engaged the cruise control. When the car went up a small incline I noticed it slowed by at least 3 MPH. When it went down the same small incline the car sped up by 3+ MPH. Even visually flat surfaces made the cruise go up and down.I thought I was doing something wrong. I pulled over, checked the manual but found nothing. I continued driving. When the car came to the first hill it sped up past 5+MPH going down the hill. When the car reached the bottom, never having slowed, the engine revved up to 3-4rpms and jerked me forward in the seat to slow the car. But the engine didn't stop at the cruise speed setting. It jerked the car below the cruise speed by 3MPH then sped up to 'near' the cruise speed, never hitting the mark. The engine varies cruise control speeds by 8MPH min when engaged. I would definitely get a ticket if I relied on the car's cruise control to establish my speed maximum. Throughout my drive of 45 miles I left the cruise engaged whenever possible. My objective was to determine the scope of the problem and to be accurate in reporting it when I took the car in for repair. A new car, requiring repair.

I made an appointment and took the car in the next week at 285 miles on the odometer. I explained what I'd experienced and stated that the cruise was not operating properly, assuming the service person would fix it. I asked him to drive it up and down hills for the best result. They drove it--somewhere--and pronounced the cruise control just fine. I've driven many, many makes and models of cars in my life with cruise control. I've never, even once, experienced this in a car--especially a brand new one. Prior to the car's return to me I'd gone on the internet to find out if anyone else has experienced this problem. YES. I handed the service person several complaints I'd printed-out which cut across Hyundai models. It was clear he didn't expect someone to come to him with printed information. The guy finally offered a lame explanation. He said it was because the car was a 4-cylinder and was shifting gears on hills. I responded, no. I am driving a 4-cylinder right there pointing to my rental and it has no problems with the cruise control. I own another 4-cylinder and it has no problems with its cruise control. I've driven 4-cylinders of various makes and models all my life with no cruise control issues. So, what gives with the Hyundai? He had no answer except to duck and repeat the corporate line which was--Hyundai didn't have any recalls on cruise control, it threw no codes and the manager drove it, pronouncing it just fine. I asked, "So the manager experienced no variation in the speeds when the cruise control was engaged?" He said well, maybe 1-2 MPH difference but that's how the engine works. So, they admitted the control didn't hold the speed but did so by downplaying the problem. Anyone not on the Hyundai payroll would immediately say there was a problem.

So, my husband called Hyundai Consumer Support, discussed the problem and filed a complaint. They said someone would call us back. That call came today after the car was in yesterday. A young women tells me that my complaint has been passed on to her. She had me repeat why I was making a report. I did. I told her the service person said it was a 4-cylinder issue, which I roundly debunked to them and again to her. She goes on to tell me she has the report and the service dept. says the cruise is operating just fine, (what am I talking to myself here?). I said, I'm aware and that is simply not accurate. She argued with me a bit about the facts ending with something like, if that's what they told you about how the engine operates then it does, or some such BS. She wanted me to take the car to another dealer for a "second opinion". I'm going to take the car to another Larry Miller Hyundai dealer, waste my time/effort simply to have them repeat the exact corporate line? Larry Miller is the ONLY dealer in Albuquerque. I said no, I have already done this. You have the report. Bottom line: If Hyundai doesn't trust one manager what makes another one in the same company under the same corporate umbrella any better or different? She then asked what I "expected" as the outcome. I said, if it can't be fixed, given the service department's inability to recognize a problem, I want my money back--all of my money. She immediately and flatly stated, "We can't do that at this time." I said "Then, why are you calling me?". I said thank-you, goodbye and put the phone down.

This car is a new 2018 with less than 300 miles on the odometer. I DID NOT purchase the "acceptable variance cruise control package". I was sold a car with cruise CONTROL (the operative word is control) not cruise variance, (i.e. it doesn't work). I did not get what I paid for, nor what I was sold. I got screwed by Hyundai corporate and their dealer, Larry Miller. I want my money back--all of it.