2018 Kia Optima: misfire or rough idle

Filed Apr 28, 2026 · Engine · VA

2018 Kia Optima LX, 2.4L GDI Theta II engine. Approximately 128,000 miles. Reporting severe internal oil consumption that has progressed to engine misfire and shaking, consistent with late-stage Theta II connecting rod bearing failure. The vehicle is now unsafe to drive and has been parked. Timeline: Purchased as a Certified Pre-Owned vehicle in December 2021. Excessive oil consumption began shortly after purchase. For approximately 4.5 years I have added about 1 quart of oil every 2 weeks to keep the engine from running dry. No external leaks have ever been found by any mechanic. Multiple independent mechanics attempted diagnosis and repair over this period. None resolved the issue. The vehicle has now developed a pronounced shake and apparent engine misfire, the textbook progression to rod bearing failure documented in the federal safety agency investigation PE19-004 and prior recalls/campaigns 17V‑224, SC147, and SC172. Safety concerns: Sudden engine seizure or stall at highway speed creates a serious crash risk for me and surrounding traffic. Theta II 2.4L GDI rod bearing failure has been associated with under-hood fires. The defect develops gradually with no warning to the driver beyond elevated oil consumption, which is frequently dismissed as normal until catastrophic failure occurs. I am filing this complaint to document the failure and to add to the federal safety agency's data on the Theta II GDI 2.4L engine in 2018–2019 Optimas. This model year was excluded from the original 2017 recall but is included in the Hyundai and Kia Engine Litigation class settlement and the lifetime engine warranty extension. My vehicle's symptoms match the defect pattern exactly. I will pursue warranty engine replacement, but I want this safety failure on the federal record regardless of how Kia responds.

Filed Sep 17, 2025 · Engine · MO

Car would convulse and shake very wildly metal parts spread around engine. It has very rough idle. 4th cylinder went out and car only has about 99060 miles. The valve went out. My safety was very bad as car was not driving safely and shaking like a person having a seizeure each time it would stop. Vehicle has been inspected by a Kia dealer. This problem I had seems to get an issue many other people with Kia Optima have.

Filed Jul 18, 2025 · Engine, Fuel system · GA

My 2018 Kia Optima LX began using excessive oil (>3 quarts/1000 miles) just over 100K miles. I researched and found that the Theta II engine in my car is known for this. When I took my car to dealership (Stokes Hodges Kia, North Augusta, SC), with the check engine light on, they told me me plugs were fouled (they were just replaced 1 yr prior), cylinder 3 misfiring, and that I needed to pay a few thousand dollars to have repaired. When I asked them to guarantee the soaking process they recommended, they responded that they couldn't, that it "only worked 80% of the time." I have the KSDS download since 2019 and asked them to follow the guidelines of their TSB ENG 222 for the class action lawsuit and start a 1000 mile oil consumption test. they refused, basically telling me the only way to get a new engine from Kia, since my car is over 100K miles, is to drive it until the engine seizes. I expressed my fear for personal safety, but they wouldn't help me. I am original owner and have all services, etc documented. I called Kia customer affairs, then was told only local dealership could help. they stuck me in a loop between them without helping. Please help me.

Filed Jul 15, 2025 · Engine · CA

Kia is aware of the engine oil consumption causing misfires, failed emissions test, blowing a rod and engine lock up. Their solution was a class action lawsuit that state once the car is locked up or rod has blown through the engine then they will fix it. I have had to add oil at least 3 times every 3000 miles and continue to replace the oil filter as well. The spark plugs have been replaced mutliple times also to help with this issue. Kia advised that my vehicle did not fall under this recall even though my vehichle is having the same issues as the recall states. This is a known issue with this make and model and they should not be able to get away with selling defective vehicles and not repairing the issues they knew they had prior to selling the vehicles. Something needs to be done.

Filed Jul 3, 2025 · Engine · OH

The 2.4L Theta II engine in my 2018 Kia Optima is failing, exhibiting excessive oil consumption, with oil loss documented at over 1 quart per 1,000 miles, leading to secondary failures in the catalytic converter, clogged with oil carbon and breaking into pieces that may damage the cylinder walls, and the spark plugs, which are fouled with carbon, causing misfires. The engine and related components remain intact and un-repaired, pending Kia’s required 3,000-mile consumption test. Safety of drivers have been put at significant risk. The excessive oil consumption and potential engine seizure threaten sudden loss of power, especially on freeways where car fails to accelerate to city and highway speeds, increasing the chance of a collision. The clogged catalytic converter poses a fire hazard, (reported by the federal safety agency investigations into Theta II) where oil leaks or debris can ignite on hot surfaces. Risk is heightened during the mandated 3,000-mile test as well. Problem has been confirmed by both a dealer and an independent service center as recent at 1 July, '25, documenting oil loss and new engine recommendation. Symptoms began with noticeable oil loss during oil changes, starting at least 1 quart per interval on May 10, 2023 (mileage 43,374), with the loss increasing over time. Misfires and RPM loss during acceleration first appeared after the oil valve gasket replacement in late May 2025, and freeway pickup issues became apparent around mid-June 2025. The full engine failure was confirmed by Spitzer on July 01, 2025.

Filed Apr 3, 2025 · Engine · VA

Kia is aware of the engine oil consumption causing misfires, failed emissions test, blowing a rod and engine lock up. THEIR SOLUTION WAS A CLASS ACTION LAWSUIT THAT STATE ONCE THE CAR IS LOCKED UP OR ROD HAS BLOWN THROUGH THE ENGINE THEN THEY WILL FIX IT. I have had to replace the spark plugs multiple times in last 12 months due to misfires while driving. I HAVE BEEN TOLD BY THE DEALER THAT THEY CANT DOING ANYTHING TO HELP EVEN THOUGH THEY ARE AWARE THEY SUGGEST THAT I DRIVE WITH NO OIL AND LOCK THE ENGINE UP EVEN THOUGH IT COULD CAUSE A CRASH. MY LIFE SHOULD NOT BE PUT IN DANAGER FIRST IN ORDER FOR THEM.TO FIX THE ENGINE.

Filed Mar 27, 2025 · Engine · 100,000 miles · SC

The contact owns a 2018 Kia Optima. The contact stated that while driving at various speeds, the contact noticed an abnormal oil consumption. The check engine warning light was intermittently illuminated. The vehicle was taken to a local dealer, where it was diagnosed with a spark plug misfire. The vehicle was repaired; however, the failure persisted. The vehicle was towed to a local independent service center, and the spark plugs were replaced. The contact stated that the vehicle was taken to a local independent mechanic where it was repaired several times; however, the failure reoccurred. The vehicle was taken to a second local independent mechanic, where the spark plugs and other unknown repairs were made. The manufacturer was made aware of the failure. The failure mileage was approximately 100,000.

Filed Feb 25, 2025 · Engine · TN

Complaint-Car misfired, oil leaking on spark plugs causing an Engin Replacement that was first complained to Gossett Kia Covington Pike,1900 Covington Pike, Memphis, Tn 38128 on [XXX].On [XXX] complaint car shakes, misfire. Complaint to Gossett Kia South 2680 Mt.Moriah Rd, Memphis, Tn 35115. This date car stayed at dealership 3 days invoice a diagnostic was performed total amt $913.38. On 12/26/24 Mr.Macias on Mt.Moriah asked me to bring my vehicle in for another diagnostic test, amt to be charged $251.00 this time a tune up, replaced #4 spark plug that had misfired, fuel injectors cleaned I asked Mr.Macias "why would I have that done when it had been done the month before, the Tech recommended Engine Replacement. I also asked the above, what about the Tech's findings, Mr.Macias stated he would get back with me. On 1/16/25 Mr.Macias called to discuss Engine replacement (Projected Amt:$6,300). I have contacted Kia Consumer Assistance on 1/10/25 to discuss all of the above to no avail. I have been without a vehicle since 12/3/26 I am continually getting the run around, I have all invoices to verify my dilemma with a vehicle that is sitting unused. I am a [XXX] who is still making a $484.00 car payment per month. I've done my research on the 2018 Kia Optima's, only to find that the same problem that I'm having with the oil leaking on the spark plugs, misfiring , shaking, causing stalling in the middle of traffic, if this is not a hazard, what is ? This a problem that should have been corrected long ago. I would appreciate it if you would please help me. I'm tired of having to pay to get to and from Dr's. Office visits, drug stores and grocery stores. Thanking you in advance, [XXX] [XXX] or email address : [XXX] INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

Filed Jun 7, 2024 · Engine · CA

Code P-030300 was detected when doing a diagnostic on my car when the check engine light came on. It is a cylinder 3 misfire. When the car comes to a idle the car starts to shake roughly. I took it to the KIA dealership I bought the car from and they told me I would need a new engine and not to drive it.Thankfully nothing bad happened while my baby was in the car. I drove it home and stopped driving it completely once the issue occurred.

Filed Apr 27, 2023 · Engine · MO

My car engine burns oil EXCESSIVELY. After an oil change, 2 weeks later i had to put more oil in. The dealership is no help even with a warranty. The car burning oil is also causing other mechanical problems that are a hefty price that are only a temp fix. I have to put oil in every single week. 2-3 quarts a week. Due to the oil being burnt off, it has affected my spark plugs and has caused a misfire in the same exact cylinder for when it misfired for this same problem, a year prior. I took it to a kia dealership last year and they performed a combustion chamber cleaning ($650+) and it only worked for 3 months before my car was back to performing poorly due to power loss from misfiring again. This car has put me in a VERY TOUGH financial situation and the dealership and corporate are absolutely no help. a year apart, this car has misfired on the same cylinder twice. the dealership just tells me to do a combustion cleaning but due to it being very pricy and with how much oil i have to buy, it’s not an option for me due to my financial situation. right now i’m just hoping something will be done for the millions of people that are effected by this.

Filed Sep 27, 2022 · Electrical, Engine · AZ

Rough idle, chugged along before killing engine power. Has happened a couple of times. No check engine light has come on