2018 Hyundai Elantra: misfire or rough idle

Filed May 22, 2026 · Engine · AZ

Engine has consumed an alarming rate of oil for years. I brought to a mechanic and they performed a $2,600 repair on engine. It ran fine for while and got much worse with oil consumption to the point that I needing to add oil monthly. It has been difficult to keep up on keeping enough oil in car and engine has now sustained damaged. There is no ticking or noise, but there is a loss of power and sometimes, the engine runs rough. I continue to drive it and add oil. But I have researched this is an apparent problem with the elantra.

Filed Nov 16, 2025 · Electrical, Engine · GA · crash · 1 injury

Initial Fault Code: P0303 Replaced all 4 spark plugs and all 4 ignition coils. The check engine light extinguished momentarily but returned, logging P0303 and a new P0301 Replaced all 4 fuel injectors. CEL extinguished momentarily and then returned, logging P0303. Replaced the entire engine electrical harness. Concurrently, all related electrical components and connectors were meticulously cleaned with professional contact cleaner. CEL extinguished for significantly longer period of time, and then returned, re-logging P0303 and P0301. Thid suggested the ECU was "handshaking" with new components but re-logging the fault upon detecting the persistent core issue. A full compression test was performed. All cylinders reported results within specification. Using a borescope I inspected cylinder walls in piston tops. There was significant carbon residue buildup but nothing out of the ordinary for similar GDI engines. I still performed a PEA GDI specific chemical cleaning. It was a a little smoother afterwards, but the misfire persisted and CEL remained on. I also removed, cleaned, and tested common sensor faults, with no result. Also p0128 code and no start / electrical drain, and engine light started flashing numerous occasions had to stop the vehicle. I tried swapping the coils, but all that proved was that the coil was good, I did a power and ground test, it passed the connector had 12 plus volt power and a perfect resistance to static ground. The signal wire from the coil connector had perfect continuity to the ECU but had OL to chassis ground showing there was no short. A test light was used to see if anything was coming from the signal wire to the ignition coil and that test failed, there was no signal pulse. The diagnostic process has definitively proven a component-level failure inside the engine control unit. See attached file for more detailed information.

Filed Aug 3, 2025 · Engine · NC

Burning oil. Multiple misfires. Replacing spark plugs more often than should have to. Engine knocking.

Filed Jul 23, 2025 · Engine · WA

I started my vehicle and it was running sluggish and low idle. I had an engine light and when I tried to drive there was a clanking sound. When I had the engine light tested I received the following codes: P0017 - Crankshaft Position Correlation Bank 1 Sensor B, P0303 - Cylinder 3 Misfire Detected, P0302 - Cylinder 2 Misfire Detected, P0301, P0014 - Exhaust Camshaft Position Timing - Over Advanced (Bank 1), P0030 H02S Heater Control Circuit (Bank 1, Sensor 1) I had it towed to my nearest Hyundai dealer in Tacoma, WA. After they did a diagnostic they said that they would have to replace the engine due to a shearing of a pin, leading to the belt jumping and causing issues. I am the only owner of the vehicle, I have had all my oil changes on time and my vehicle is 137,000 miles. This should not be happening in a vehicle with such low mileage. In reading online, this is an issue that Hyundai is aware of but not concerned with. There was no warning beforehand. This could have led to my engine stalling on the the freeway at freeway speeds and thus could have caused a great accident and bodily harm to myself and others. Hyundai has denied responsibility but knows this is an ongoing issue with it's poorly manufactured engines. I was not informed of all the problems of Hyundai vehicles before I purchased mine. I have yet to receive help from Hyundai Customer Service or the Hyundai Dealer.

Filed Jun 11, 2025 · Engine · TX

Formal Complaint: Engine Failure in 2018 Hyundai Elantra To Whom It May Concern, I am submitting this formal complaint regarding a severe and unresolved issue with my 2018 Hyundai Elantra, which has been problematic since the time of purchase and has now suffered a complete engine failure. Despite regular maintenance and responsible use, the vehicle has proven to be unreliable and unsafe. 1. Nature of the Problem The most recent and critical issue involves total engine failure. On May 12, 2025, I brought the vehicle to North Freeway Hyundai due to the car not starting. Their official diagnostic report revealed that the engine needs to be replaced. Additionally, the inspection showed issues with the transmission cooler coolant lines leaking, EFI system, camshaft exhaust, radiator hoses, and the battery. These problems affect essential systems that are critical to both the performance and safety of the vehicle. 2. History of the Problem From the beginning, the vehicle experienced a series of mechanical issues. These included engine stalling, warning indicator lights, rough idling, and decreased fuel efficiency. I consistently took the car in for service and maintenance, yet the problems worsened. In the days leading up to the failure, the vehicle had trouble starting, made abnormal noises, and eventually stopped working entirely. 3. Risk to Safety The failure of the vehicle to start without warning has placed me in unsafe and potentially dangerous situations, including being stranded in public places. The risk of the car stalling during operation could have endangered not only my safety but also the safety of other road users. This is a serious safety concern that should not be ignored. 4. Diagnosis Confirmation The diagnosis by North Freeway Hyundai confirmed that the engine failure is complete and that replacement is necessary. The service notes also included a recall campaign (24-01-009H-1) for anti-theft software and decals. These issues further demonstrate

Filed Jun 8, 2025 · Engine · TX

I am filing this Vehicle Owner's Questionnaire (VOQ) regarding critical safety defects in my 2018 Hyundai Elantra related to: - Recurrent ignition coil pack failures (3 replacements since 10/2018) - Engine stalling at low speeds (6 incidents since 10/2018) - Dealer refusal to apply TSB 20-01-008H ECM update despite matching symptoms Technical Background: Hyundai Technical Service Bulletin 20-01-008H (February 2020) specifically addresses: - Misfire detection logic flaws in 2018-2019 Elantra 2.0L engines - Required ECM software update (ROM ID AD8SP2AS673D) - Updated ignition coils (P/N 27300-2E601) Safety Incidents: 2025: Stalling event at 25 mph approaching traffic light (no crash) 2021, 2023, 2024: Multiple misfire codes (P0300-P0304) with check engine light Dealer Interactions: - Round Rock Hyundai refused ECM update on 05/2025 claiming "VIN not in campaign" - Round Rock Hyundai refused coil replacements on 05/2025 claiming not under warranty - Service advisor acknowledged stalling/coil failure pattern matches TSB criteria Formal Requests: - Investigate Hyundai's VIN filtering for TSB 20-01-008H applicability Require Hyundai to: - Perform ECM software update per TSB specifications - Replace all coils with updated P/N 27300-2E601 - Reimburse previous coil replacement costs $1700 (6 coils over 7 years) - Open recall investigation for 2018 Elantra ignition systems Attachments available upon request. I authorize the federal safety agency to share my contact information with Hyundai Motor America. This defect creates unreasonable safety risks through sudden power loss and compromised vehicle control.

Filed Apr 20, 2025 · Fuel system · FL

Fuel injectors failed at 43,000 miles and 66,000 miles with no warning. Car misfired and left me stranded.

Filed Mar 16, 2024 · Engine · FL

Unfortunately I bought a Hyundai Elantra sport brand new in 2018 i’ve kept the maintenance even to this day the car currently at 147,300miles. However I started having issues at 30,000 miles check engine would go on the car with shake and stall and miss fires would occur frequently. Every time I took it to the dealer they reset the computer but never made an actual note of what was going on with the car. That dealership that I took it at the time was Universal Hyundai in Orlando, Florida. So now that I have 147,300 miles the same misfires are now catastrophic failures on the same cylinders, to add insult to injury I took it to a different dealer located in Sanford Fl so they can try to get willful engine replacement, and my claim was denied because I was out of warranty and over the mileage, the dealership new that I was both over mileage and out of warranty the second I brought the car in somehow I still get charged $213. It seems like no one can do anything about it cause Hyundai America made there decision to deny my claim. These cars are straight up trash my buddies Kia similar situation has made it to 150,000 before he had total engine failure engine seized up on him. To make things worse I’m making payments on a car that’s needs an engine replaced. I’m never buying a car from Hyundai ever again they’re straight garbage and now I have to purchase another vehicle. Thanks Hyundai America for making unreliable vehicles and then taking my $213 to just deny my claim despite having a perfect maintenance record. I hope people read this and realize what crooks you guys are. Side note Hyundai America refused to help, however when I threatened to contact the BBB to complaint about there product the customer service agent Ciani mentioned they will open up case as to why I’m putting a complaint to the BBB, I don’t know what the outcome of this will be but it’s irrelevant I wouldn’t take a free Hyundai even if it was given to me! You lost another customer for life!!!

Filed May 25, 2023 · Engine · OH

I purchased this car as a used car at CarMax in July 2022 and it drove fine for about 10,000 miles, but starting in February 2023, my engine started to misfire. The first misfire happened when I started my car. I was told by my local mechanic that I needed a new engine after a compression test was run. My engine misfired a 2nd time while I was merging on the highway and a third time while I was starting my car. I only have 68,975 original miles on my car. The first 2 misfires illuminated the check engine light and the third misfire illuminated the check engine light, the battery light and oil pressure light, however my mechanic didn't find any codes with my third misfire. My car regularly rough idles and has a delay when I accelerate as well.

Filed Jun 16, 2022 · Engine · TX

Multiple events of engine shutoff while driving. This results in loss of power braking, power steering and any acceleration. This occurs both at highway and non-highway speeds. This is obviously a safety concern, as, until the engine is restarted, there is difficulty in safely manuevering the vehicle. The engine may or may not be immediately able to restart. This occurs with the vehicle in gear during normal driving conditions (IE, driving at a steady speed on flat road) This is accompanied by multiple CEL faults relating to CCV timing, engine misfire, etc. This was a known issue in prior engine revision (Theta 2.0L), and appears to be subject to a recall of the same engine (Nu 2.0L) in other models. This vehicle was taken to the local dealer and confirmed to need an engine replacement with a similar failure mechanism as the Theta 2.0L (failed lubrication of pistons resulting in premature wear leading to early failure resulting in misfire/"piston slap")

Filed May 29, 2022 · Engine · FL

I have been having issues with my car since November 2021. My car would not go over 35 miles per hour, if I let my car sit for a couple of days I would have to jump my car. My check engine light came on and then 10 minutes later went off. So I finally got it in to the Hyundai dealership after months of them not having enough mechanics. So they did a multipoint inspection and came back saying the catalytic converter needed to be replaced even though no codes in the system. So I was coming back from Florida when my car stopped accelerating on the highway and my check engine light. So I had to take the long way home which means no highways and anytime I stopped I had to throw my hazards on until it would pick up any speed. I took it to Jiffy Lube in SC and that's when my car was reading 8 different misfire codes so I did my tune up with them and that is when I was told that my engine valve was cracked and dumping oil on my spark plugs and coil pack. Yesterday my engine valve replaced and another set of spark plugs in 2 weeks and it is still reading misfire codes and still no change in acceleration. I have only had my car 4 years and my catalytic converter should not be gone. I have not really moved my car in 10 months because my husband passed and I had 2 surgeries. My family can't take another loss if something happens to me because of this car.

Filed Apr 27, 2022 · Engine · NC

Engine would randomly idle mild to very rough when started and would sometimes correct and sometimes not correct while driving. This would turn on the check engine light for a misfire on cylinder 4. All ignition coils were replaced, and same code would happen. Hyundai was aware of this being a widespread issue and did a software update (Tech Bulletin 90C042R1). The problem continued, but seemed the check engine light would not come on as soon as before the software upgrade. Took back to dealership and they said the ignition coils would need to be Hyundai brand, change cylinder 4 to OEM and still having the issue. Engine also burns about 1 quart of oil every 7000 miles and often has a rough idle, with very rough idle periodically. I feel this would put myself and others on the road in danger if the engine were to fail while driving due to the ongoing damage rough idling appears to be causing to the engine.