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2015 Soul+, 2.0 liter. 90k miles
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Hi, new to the forum but I'm hoping someone here has had the same issue. I have a 2015 Soul+, 2.0 liter, auto transmission, 90k miles. I'm getting some intermittent misfires when at idle when in Park and also when the car the car is in Drive stopped at a redlight/stop sign with the brake pedal depressed. It seems to happen more when the engine is warm. I haven't noticed anything unusual when the car is moving. Within the last few months I've replaced all 4 sparkplugs, the coils on cylinders 3 and 4 and the PCV valve. I had the knock sensor recall done recently as well. I haven't noticed any excess oil consumption. I've been running fuel injector cleaner 4 out of my last 6 fillups hoping it was just some gunk in an injector, but it doesn't seem to have fixed anything. This is an intermittent issue that seems to come and go. When cold, the car will idle at around 1k rpm and run fine. After its warmed up it will idle at around 600 rpm but dips to around 500 with the small misfires. Does anyone here have some advice? I'm planning on bringing it in the the dealership, but I bought it used and its out of warranty so I was hoping it might be something that I could take care of myself.
 

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To begin the process of elimination (compression, fuel, spark), suggest that you start with spark:
With new spark plugs (color of old?) and two new coils (why 3 & 4?), I'd first look for a voltage / connection issue:
1. What is charging voltage at idle?
2. What is condition of battery cables / terminals at battery?
3. What is condition of battery negative ground to body?...has it been removed, cleaned and reinatalled?
4. What is resistance of from battery negative terminal to engine?...less than 0.5 ohm?

With no oil consumption and running good, other than idle, compression is not likely an issue.

Does the 2015 model have an idle air control valve (IACV)? If so, it may need cleaning.

Are all vacuum lines intact?
 

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If you don't have a scanner get one or borrow one. You can pull up misfire data while it's running and that will tell you which cylinder is doing it. Even if it hasn't set a hard code yet it may have a pending code but it would be best to pull up data and watch the misfire counter for all the cylinders and see which one is the culprit
 

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This will also make it easier, say you're misfiring on cylinder 1 swap the coil with 3 and see if it follows the coil. If it stays on 1 swap the plug with 3 and see if it follows the plug. New plugs aren't always good especially if someone dropped it. I replaced one today on a 2018 with 15k miles on it, just one plug was bad.
 

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I just recently switched out the spark plugs on the Xterra Off-Road. I failed to properly reclip the electrical wires to the ignition coil on cylinder 5. Dumbass...... :-(

The Torque Pro app on an Android smartphone quickly identified the problematic "misfiring" spark plug and made fixing the issue much easier.


In passing, the ignition coils on the 220K 2006 Xterra are in great shape but the platinum spark plugs were due for a change. I replaced them with NGK Iridium spark plugs. The price of Iridium has recently gone through the roof so I wonder if that will get translated into more expensive Iridium spark plugs or simply less product available.
 
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2018 Kia Soul, 1.6l Auto base model.
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Might sound a little odd, but does the rpm drop with the a/c or defrost on? I was having a bit of a rough idle on my 2018, but found that it was due to those factors. Just a thought.
 

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2015 Soul+, 2.0 liter. 90k miles
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Discussion Starter #8
To begin the process of elimination (compression, fuel, spark), suggest that you start with spark:
With new spark plugs (color of old?) and two new coils (why 3 & 4?), I'd first look for a voltage / connection issue:
1. What is charging voltage at idle?
2. What is condition of battery cables / terminals at battery?
3. What is condition of battery negative ground to body?...has it been removed, cleaned and reinatalled?
4. What is resistance of from battery negative terminal to engine?...less than 0.5 ohm?

With no oil consumption and running good, other than idle, compression is not likely an issue.

Does the 2015 model have an idle air control valve (IACV)? If so, it may need cleaning.

Are all vacuum lines intact?
Thank you for the help. I noticed the car being a bit jerky with the brakes today when coming to a stop. RPM would fluctuate a bit, like it was struggling to stay running. Might all be in my head lol.

Coil #4 was replaced because it failed while my wife was driving and popped a PO304 immediately. The plugs were changed. 1-3 looked ok, just well used. The plug from #4 was black on the tip. I changed coil 3 out because I was starting to notice this rough idle issue and figured it was another coil going. I popped it into 3 and it seemed to take care of the issue, so I left it but I think that was just a coincidence because the rough idle is back.
1. Forgot to check charging voltage with my meter. My OBD scanner said it was just about 13.3 if I remember correctly. Will have to confirm.
2. Battery cables seemed ok.
3. Ground cable seemed ok as well. I replaced the battery back in November and didn't notice much corrosion, if any.
4. Resistance between the negative battery terminal and engine block was like .1 ohm. It was closer to 20 ohms from the negative terminal to the ground lug on the inside of the engine bay, I'm not sure what that indicates.

I took a look at the coils on cylinders 1 and 2 today. One of them had a minor scratch running down the side of it, which I do recall seeing on the #4 coil that had malfunctioned a few months ago. Could this be related to my issue? I would think with a bad coil it would show up immediately, not just when the engine was warm.

I check the engine air filter and there were some leaves in the box and in the filter itself but it seemed mostly clear.

As far as vacuum lines go, I wouldn't even know where to start with those to be honest.

If you don't have a scanner get one or borrow one. You can pull up misfire data while it's running and that will tell you which cylinder is doing it. Even if it hasn't set a hard code yet it may have a pending code but it would be best to pull up data and watch the misfire counter for all the cylinders and see which one is the culprit
I do have a scanner. I can't seem to access live misfire data, or maybe I'm looking in the incorrect place. To be honest, besides pulling codes, I have zero clue what any of this data means lol. Thank you for the help.
 
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