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2014 Kia Optima EX
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Discussion Starter · #1 ·
I've noticed now that when I sit idling the car will sometimes rev a little higher then drop to normal. I'm talking about a maybe 50 to 150 rpms more but definitely noticeable. Kind of like stumbling/shaking . The plugs have about 40K on them, filters are new and I change the oil every 3500 and substitute 1 quart with Lucas oil. Car has 123K it's a 2014 EX.
 

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Possibly the coils, i just went through crap with mine. Purchase them from a dealership, autoparts store sold me some non turbo ones and had me diagnosing for weeks.....was not cheap either
 

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2012 Kia Optima SX
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22 Posts
What's the temperature outside when it happens? Could be the air conditioner compressor kicking in, which in turn causes the revs to bump up to provide the additional power needed to run it.
 

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2011 Kia Optima
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The compressor is running all the time, but with or without the compressor the cooling fans could be called upon and as with any electrical draw, the engine will vary rpms.
 

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2014 Kia Optima EX
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Discussion Starter · #5 ·
The compressor is running all the time, but with or without the compressor the cooling fans could be called upon and as with any electrical draw, the engine will vary rpms.
I have this car now 4 years. Unless fans are going bad electrical draw would still be the same as it always was shouldnt it?This problem just started creeping up these last 4 months.
 

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2014 Kia Optima EX
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Discussion Starter · #6 ·
What's the temperature outside when it happens? Could be the air conditioner compressor kicking in, which in turn causes the revs to bump up to provide the additional power needed to run it.
It's been happening for about the last 4 months. So anywhere from mid 60's to below freezing. I have had this car for the past 4 years and this started like I said about 4 months ago. Someone mention electrical draw would cause variations in idling. I understand that but if it's within the normal range the car shouldn't stumble or shake when RPM changes. This stumble/shaking is beyond the norm.
 

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2014 Kia Optima EX
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Discussion Starter · #7 ·
Possibly the coils, i just went through crap with mine. Purchase them from a dealership, autoparts store sold me some non turbo ones and had me diagnosing for weeks.....was not cheap either
Anyway to test coils before replacing them? I had a misfire on my old 300M that was caused by a bad coil but it threw a code/ check engine light. Would the self diagnostic via UVO detect a bad coil? It always says it found no critical issues.
 

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2014 Kia Optima EX
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69 Posts
Discussion Starter · #8 ·
I just want to say thank you to everyone who responded with their suggestions. If anyone has anything else to add please feel free to. Thanks again and everyone stay safe and healthy.
 

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2012 Kia Optima SX
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The compressor is running all the time, but with or without the compressor the cooling fans could be called upon and as with any electrical draw, the engine will vary rpms.
This isn't true. The pulley on the compressor is being turned all the time, but there is an electromagnetic clutch that engages and disengages the compressor, and the compressor will engage/disengage while the A/C is running to maintain temperature. With the clutch disengaged, the pulley puts no more load on the engine than a tension pulley would. With the clutch engaged, the compressor requires ~3 horsepower to run, thus causing the car to increase its idle revs.
 

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It's been happening for about the last 4 months. So anywhere from mid 60's to below freezing. I have had this car for the past 4 years and this started like I said about 4 months ago. Someone mention electrical draw would cause variations in idling. I understand that but if it's within the normal range the car shouldn't stumble or shake when RPM changes. This stumble/shaking is beyond the norm.
I'm assuming your EX is the 2.4L engine? Could be carbon buildup on the valves after so many miles causing it to be a bit rough. 40k miles on the spark plugs should be fine, but there's a chance they're getting a little worn that could cause this. Electrical components like a cooling fan could be starting to wear, which means there's more mechanical resistance and requires more power to operate. The fact that you say the car is not only increasing in idle, but it's noticeably rougher leads me to think it's something not electrical now though.

Have you ever cleaned your throttle body? It could have some deposits on it so it's not performing optimally. It's pretty simple to get to the throttle body to clean it.
 

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2014 Kia Optima EX
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Discussion Starter · #11 ·
Thanks for explaining that. So that would mean either a bad pulley or bad clutch? The RPM's actually drop not rise in my case causing the stutter/stumble.
 

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2014 Kia Optima EX
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Discussion Starter · #12 ·
Had the engine cleaned once around 60K. One of those services they sell at the local oil change place. I have never cleaned the throttle myself. I do use regular but only name brand gas. When ever I have an oil change, every 3k, I have 1 qt oil replaced with 1qt Lucas additive. Well these are things to consider. My only concern is that you mention a rise in RPM, the opposite of what I am experiencing.
 

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2012 Kia Optima SX
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I must've misread, I missed that you said the revs were dropping, not increasing. If they're dropping, it could be a number of things. Could be a vacuum leak, could be a bad or dirty EGR valve, could be spark plugs/coils, could be a dirty fuel line if you're not using TopTier gas (I'd dump a bottle of cleaner in at your next fuel fill when you're under 1/4 tank. Some claim it's snake oil, some are diehard to a brand. I use Techron, but have also used Seafoam and CRC).
 

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2011 Kia Optima
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This isn't true. The pulley on the compressor is being turned all the time, but there is an electromagnetic clutch that engages and disengages the compressor, and the compressor will engage/disengage while the A/C is running to maintain temperature. With the clutch disengaged, the pulley puts no more load on the engine than a tension pulley would. With the clutch engaged, the compressor requires ~3 horsepower to run, thus causing the car to increase its idle revs.
Please check before writing something that is untrue. The compressor is a VDC and there is no clutch so internals turn all the time. The electronic control valve at the back of the compressor changes the position of the swash plate and that increases or decreases the piston displacement and the result, more or less cooling depending on demand, but the compressor is running all the time.

It's been happening for about the last 4 months. So anywhere from mid 60's to below freezing. I have had this car for the past 4 years and this started like I said about 4 months ago. Someone mention electrical draw would cause variations in idling. I understand that but if it's within the normal range the car shouldn't stumble or shake when RPM changes. This stumble/shaking is beyond the norm.
I agree, now knowing the ownership has been 4 years, something has changed, but I'd say not in the ignition system, nor the fan(s) as they have been functioning for the last 4 years. A real time scanner would work wonders as all systems could be monitored for fluctuations.

See it's a turbo so check the air intake air system for any leaks, clamps, intercooler etc.
 

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Anyway to test coils before replacing them? I had a misfire on my old 300M that was caused by a bad coil but it threw a code/ check engine light. Would the self diagnostic via UVO detect a bad coil? It always says it found no critical issues.
A faulty coil sometimes doesnt really throw cel. Mine was/is so bad that i couldnt accel heavily. (Explained in another thread) but once i swapped 2 of oe coils that were still functional, i could accel just fine. Still bit of rough idle since i need other 2 coils. Overall, if you have an obd scanner, you may be able to see if any of cylinders are getting a misfire count. Honestly ive noticed optimas love to mess up in cylinder 2 the most.
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Highly unusual/unlikely that any car needs all 4 coils.
Normally any problem that attacks, or involves multi-cylinders is an upstream
problem unrelated to coils or plugs.
 

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2014 Kia Optima EX
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69 Posts
Discussion Starter · #17 ·
Well I was able to get 4 OEM coils for $84 total and I ordered a Bluedriver OBD2 scanner. Lets see what happens.




A faulty coil sometimes doesnt really throw cel. Mine was/is so bad that i couldnt accel heavily. (Explained in another thread) but once i swapped 2 of oe coils that were still functional, i could accel just fine. Still bit of rough idle since i need other 2 coils. Overall, if you have an obd scanner, you may be able to see if any of cylinders are getting a misfire count. Honestly ive noticed optimas love to mess up in cylinder 2 the most. View attachment 248090
 

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2014 Kia Optima EX
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69 Posts
Discussion Starter · #19 ·
A dealer on Ebay was offering them for $19.99 each with free shipping. Since they had a "make an offer" option I got them for $19.50 each.
 
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