2012 kia rio randomly jerks


The car will randomly jerk when accelerating slowly. Sometimes once. Sometimes a couple times. I don’t hear anything weird. The spark plugs are good. The previous owner said he replaced the ignition coils. Any suggestions?

any check engine light? codes?
manual or automatic transmission?

automatic and no codes

Does your scanner read transmission codes? Also low transmission fluid can cause this. So far I’m guessing this is transmission related.

it does not.

That’s one of the early signs of a crank sensor that’s starting to fail.



that is what I was thinking but wouldn’t it give a code?

Awesome that would be an easy fix. Do you know if they usually go out slowly?

Sometimes they fail all at once and the engine shuts off and won’t restart.



I took it on a long drive. It does it going up hills quit a bit. Would a crank sensor do that?

Are the spark plugs the OEM type? I know you said they were “good”…but sometimes weird things happen when folks try to “upgrade” the spark plugs.

Like random jerking, due to misfires.

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I wouldn’t think the crank sensor would care if the engine had a load on it or not, like when going up a hill. I have had that happen when I needed new plugs, though. Light misfires when the engine was under a heavy load going uphill in overdrive, but not enough for the check engine light to set. Would be ideal if you could check for misfires. May be cheap coils, coils installed poorly, some crazy aftermarket plugs installed, etc. I wonder why the previous owner replaced the coils in the first place. Was he trying to resolve this issue?


I checked on amazon and saw they are the right type. They were not cheap. I also checked the gap.

I’m assuming so. I found it on facebook marketplace. I did not notice it at all when I bought it. I feel like its gotten worse over the past week. Is there a practical way to check for misfires?

does it happen more on rainy days? or the same all the time? if it happens more on rainy days then its probably electrical. like a bad coil

I live in Northern California. I haven’t seen rain in quit a while.

I’ll have to let the real mechanic’s answer as to what level tool you’d need, but a scanner would show misfire counts and tell which cylinder(s) are misfiring, if any.

Are the coils a decent brand also?

you said you took it for a long drive and it did it again. check it for codes again. it might have a soft code that does not put the check engine light on.

thanks ill do that now