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Ron Z.
Ron Z., - Hyundai Tech -
Category: Hyundai
Satisfied Customers: 18866
Experience:  18+yrs experience. State Inspector and Hyundai Diagnostics
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I have a 2009 Sonata. It suddenly developed a rough idle and

Customer Question

I have a 2009 Sonata. It suddenly developed a rough idle and acceleration. Seems almost OK at constant speed. Thought it was running on 3 cylinders, so I replaced the plugs. Only a slight improvement. Check engine light is on. 93,000 miles. If EGR issue, does Hyundai cover under the 100,00 mile warranty?
Submitted: 1 year ago.
Category: Hyundai
Expert:  Ron Z. replied 1 year ago.

From what you are describing here, it sounds like a cylinder misfire. If the plugs helped a bit but not much, I'd lean more towards this being a problem with one of the Ignition Coils or a faulty or clogged Fuel Injector. If this was an EGR problem, it would not have happened "suddenly" so I think we can rule out the EGR here. Best bet at this point would be to have the Diagnostic Trouble Codes (aka "P-Codes") retrieved from the on-board computer. You can have these p-codes read FREE (except in California) at any local "big chain" part store (ie. AutoZone, PepBoys, Advanced, etc). These p-codes will better help us determinethe root of the problem. For example, if the problem "is" an ignition coil-0 which one? No need to replace them all if only one is faulty. Same with the fuel injectors "if" that's where the p-codes point. Ignition coils are a fairly common fail item. Unfortunately, not quite sure what the warranty will cover as I do not have access to that type of information. That would be something to discuss with the warranty company. However, as far as I know, I do not believe these are covered as they are considered normal wear-and-tear items (like brakes and spark plugs, etc). Please remember to leave a rating using the star rating system at the top of this page or accept the answer so I may be credited for this Q&A. You can ask follow-up questions any time, even after you rate or accept.