Need help - '14 CX-5 rough engine idle after replacing spark plugs

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2014 Mazda CX-5
Hey All,

Quick background on issue:
Saturday morning, car started up fine with no issue and after a few minutes of driving, as i go to turn onto the highway, all of a sudden it felt like i had a flat tire. So i kept driving a couple of feet and then the Traction Control, Tire Pressure, and Check Engine light came on all at once. I drove to the nearest gas station and popped the hood to see if anything was wrong, and oil was fine, coolant was fine, etc. So with all 3 lights on, i slowly drove it home which was about 5ish minutes away. In that time, the car was in limp mode and would not go above a certain speed. I get it home, park it, and leave it for a day to rush to an important event.

The next day, i put the ODB reader in and i got the error P0304 that indicated a misfire in Cylinder 4. Looked online and saw that cause could be due to spark plugs, which with 110K miles and having never been replaced, i went with that diagnosis for my situation.

Hopped on Amazon and ordered new spark plugs, specifically NGK 94124 that have been recommended on this forum and other places as being identical, if not the same as OEM. Didn't touch the spacing as it was also said the default spacing they come with is correct for Mazda and no adjustment is needed.

So i eventually was able to get them all replaced, and started the car, and all the lights were now gone. I put the ODB reader back in and no additional codes or pending codes showed up, so i figured all was good. Car started alot better than it did previously.

Only issue is, the engine still has a rough idle in park and when in drive, and the exhaust has a put put put noise that i never noticed previously.

Questions
1. Any idea what could still be causing the rough idle when in park and stopped in drive, as there are no dash warning lights lit up pointing to anything?
2. Could i have damaged the catalytic converter or something else when i drove it from the gas station to home with the CEL on?

Planning on getting it towed to the shop for diagnosis next week if i can't figure it out.

Appreciate any help or info.
 

erhayes

Contributor
:
Mazda CX-5 FWD Touring
I would disconnect the battery for 15 minutes or so and reconnect. This will reset the engine computer to the default settings. Ed
 
:
2014 Mazda CX-5
I would disconnect the battery for 15 minutes or so and reconnect. This will reset the engine computer to the default settings. Ed
Thanks. The battery was disconnected while i replaced the spark plugs, so the engine computer should have reset then, no? or do you suggest i disconnect again?
 

erhayes

Contributor
:
Mazda CX-5 FWD Touring
No need to disconnect the battery again. . I would drive it for 10 + miles and see if it improves.
 
:
2016 CX-5
You might have a foreign object stuck in there.

I once had an intermittent rough idle after dealer service and it eventually threw a P0015 code.

It is associated with a TSB: https://mazda.oemdtc.com/542/rough-idle-with-the-mil-on-and-dtc-p0015-p0524-2012-2016-mazda

Thankfully I was in warranty so I didn't have to debate if dealer service caused the issue

Your situation sounds worse, but perhaps try the first line in the TSB: "Depress the throttle pedal and momentarily adjust the engine speed to 4,000 rpm or more for 10 times."

Good luck
 
:
2014 Mazda CX-5
You might have a foreign object stuck in there.

I once had an intermittent rough idle after dealer service and it eventually threw a P0015 code.

It is associated with a TSB: https://mazda.oemdtc.com/542/rough-idle-with-the-mil-on-and-dtc-p0015-p0524-2012-2016-mazda

Thankfully I was in warranty so I didn't have to debate if dealer service caused the issue

Your situation sounds worse, but perhaps try the first line in the TSB: "Depress the throttle pedal and momentarily adjust the engine speed to 4,000 rpm or more for 10 times."

Good luck
Thanks, not sure if this would be related though as i don't have any check engine lights on.
 
:
2014 Mazda CX-5
No need to disconnect the battery again. . I would drive it for 10 + miles and see if it improves.
Thanks, i'll try that and see what happens. If anything, hopefully it would throw another error code if anything was seriously wrong.

Are there occasions where an engine would need to adjust to new spark plugs?
 
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Mazda Protege DX
Ummmm, obviously do not drive it with a obvious misfire... Was it running fine with old plugs? If so switch it to the old ones, if vehicle runs fine you know the new plugs are no good.

I believe skyactiv takes those iridium plugs, not the cheap shit ones so if it runs fine on old plugs it is obvious you need to get different plugs.

No matter how much you reset or disconnect battery, a misfire is a misfire right? So try that first
 

yrwei52

2016 Mazda CX-5 GT AWD w/Tech Pkg
Contributor
:
Plano, Texas, USA
Thanks, i'll try that and see what happens. If anything, hopefully it would throw another error code if anything was seriously wrong.

Are there occasions where an engine would need to adjust to new spark plugs?
I’d try the battery disconnect reset again, wait for 10~15 minutes. While waiting, pull all new plugs and check the gap even though it’s not supposed to be adjusted.

For spark plug gap, on PE5R-18-110, PE5S-18-110:
Standard: 1.05—1.40 mm {0.0414—0.0551 in}
New spark plug (reference): 1.05—1.15 mm {0.0414—0.0452 in}

Although it’s unlikely, but there’s still a chance you got a defect plug or counterfeit NGK plugs which would cause some problems.

Lastly, check the engine and transmission mounts and see if there’s any leaks.

If your only symptom is rough idle, just drive the CX-5 for a couple of weeks and see if there’s any error codes being generated. Even if you want to resolve the issue quickmy, you don’t have to get it towed to the shop for diagnosis, just drive there. And most shops or even Mazda dealers, can’t do much on a vehicle anyway nowadays if there’s no error codes.
 
:
2016.5 CX-5 GT AWD titanium/black 2016 Miata Club ST MT white
How did the old plugs look after removing them?

Any chance that you may have damaged a plug wire or one of the coils in changing the plugs?
 
:
Pueblo county CO
:
CX-5 Sport 16.5 6M
It is pretty strange if it was running fine then this sudden change.

Did anything happen the day before, or the previous drive?
 

mazdadude

ZOOOOOOOOOM ZOOOOOOOOOM
:
'16.5 Mazda CX-5 Touring
It is pretty strange if it was running fine then this sudden change.

Did anything happen the day before, or the previous drive?
I agree... I would not be messing with the plugs again, or bother removing to check gap.

Because you disconnected the battery, the car will have to relearn fuel mapping.

Extra vibrations at idle in park can be caused by failed motor mounts.

Out of curiosity, did this all happen after the last time you refueled?

If it was my car, I would: 1. inspect the motor mounts for the cause of the vibrations as they are a known failure point. 2. Since there is no more misfire or limp mode, drive it for a few cycles and see if there are any more codes or check engine lights.

It always kills me how some of the responses show that there is very little reading comprehension involved. :)
 
Last edited:
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2014 mazda cx-5 touring FWD
I don't remember anything regarding the motor mounts on a 2014 as being a failure point.Where is this mentioned/discussed? Thanks. Jmaz
 

mazdadude

ZOOOOOOOOOM ZOOOOOOOOOM
:
'16.5 Mazda CX-5 Touring
I don't remember anything regarding the motor mounts on a 2014 as being a failure point.Where is this mentioned/discussed? Thanks. Jmaz
Sorry for the misunderstanding I never said they were a failure point on a 2014, however they are a common failure point and cause of rough idling issues on any of the Mazdas that use the hydraulic motor mounts post 2004
 
:
2014 Mazda CX-5
I’d try the battery disconnect reset again, wait for 10~15 minutes. While waiting, pull all new plugs and check the gap even though it’s not supposed to be adjusted.

For spark plug gap, on PE5R-18-110, PE5S-18-110:
Standard: 1.05—1.40 mm {0.0414—0.0551 in}
New spark plug (reference): 1.05—1.15 mm {0.0414—0.0452 in}

Although it’s unlikely, but there’s still a chance you got a defect plug or counterfeit NGK plugs which would cause some problems.

Lastly, check the engine and transmission mounts and see if there’s any leaks.

If your only symptom is rough idle, just drive the CX-5 for a couple of weeks and see if there’s any error codes being generated. Even if you want to resolve the issue quickmy, you don’t have to get it towed to the shop for diagnosis, just drive there. And most shops or even Mazda dealers, can’t do much on a vehicle anyway nowadays if there’s no error codes.
Thanks, i'll try driving it a bit and see if there are any changes. Main concern with that was i didn't want to potentially cause damage to anything like the catalytic converter, especially since there are no lights on and wouldn't know. I'll give it a go.
 
:
2014 Mazda CX-5
It is pretty strange if it was running fine then this sudden change.

Did anything happen the day before, or the previous drive?
To be honest, no. The car was running fine and besides the slight hesitation every now and then that i mentioned, everything was running completely fine. as soon as i turned on to that on ramp, it came out of no where.
 
:
2014 Mazda CX-5
I agree... I would not be messing with the plugs again, or bother removing to check gap.

Because you disconnected the battery, the car will have to relearn fuel mapping.

Extra vibrations at idle in park can be caused by failed motor mounts.

Out of curiosity, did this all happen after the last time you refueled?

If it was my car, I would: 1. inspect the motor mounts for the cause of the vibrations as they are a known failure point. 2. Since there is no more misfire or limp mode, drive it for a few cycles and see if there are any more codes or check engine lights.

It always kills me how some of the responses show that there is very little reading comprehension involved. :)
Thanks, I'll check the mounts and see whats going on there. I have somewhere to go tomorrow, so i'll take it for a spin and see what happens.
 
:
2014 Mazda CX-5
Thanks for the assist guys, i'll disconnect the battery again and then take it for a spin (most likely 5+ miles), can report back if any new lights pop up.

Definitely strange to come out of no where.

but one more quick question, could rough idle be caused if the spark plugs were put in to tight? I don't think i overtightened but you never know, and just want to rule that out as a possibility.
 

yrwei52

2016 Mazda CX-5 GT AWD w/Tech Pkg
Contributor
:
Plano, Texas, USA
Thanks for the assist guys, i'll disconnect the battery again and then take it for a spin (most likely 5+ miles), can report back if any new lights pop up.

Definitely strange to come out of no where.

but one more quick question, could rough idle be caused if the spark plugs were put in to tight? I don't think i overtightened but you never know, and just want to rule that out as a possibility.
The torque spec on spark plug for 2.5L is 12~14 ft/lbf. This’s very low on torque and it’s very easy to overtighten them. No, overtighten the plugs won’t cause the rough idle, but may have a great chance to damage the thread on cylinder head.

The reason why I suggested you to check the plug gap is the factory preset gap sometimes may get changed during the shipment. This happened to me once and that’s how I know. And I always double-check the gap on new spark plugs before installation.
 

AVC

:
'17 CX-5 Select
A couple of thoughts; 1) unless you got the plugs from RockAuto or another reputable automotive supplier, beware of a number of Chinese fake, poor quality NGK and Denso labeled plugs that have appeared on Amazon, Ebay and other third party sellers. 2) unless you broke/cracked the plugs or stripped the holes while installing, that's not the issue. 3) unless the plugs you removed were in horrible condition and had wide gaps, that probably wasn't the original or current issue, either. 4) the "sudden" limp mode may have been an ignition coil on it's way out, which showed up during hard acceleration. 5) If there are indeed lots of misfires, it'll ruin your cat in short order. If you have a scan tool, check the misfire counts at the end of a drive, before shutting the car off.
 
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