Car rpm dropping, car jerking while idle

I have a 2014 Kia Forte that I purchased used about a year ago. I have had issues with it jerking (I thought I was rear-ended the first time it happened) while I am sitting at idle. It doesn’t matter if I am in drive, neutral or park. It also doesn’t matter if the AC is on or off. I took it to the dealership the first time, and they replaced a spark plug and coil pack. It seemed to do fine, but I recently changed the spark plugs and now the issue is back. Is this going to require replacing all of my coil packs? Is there something that could keep causing everything to go out? I know nothing about cars, and I don’t really make enough to bring it to a mechanic every time this happens.

First, have the codes read, usually free at most auto parts stores. Then post the codes back here.
A proper diagnosis is usually less expensive than throwing random parts at a problem.
Please explane what you mean by jerking. Unless you have a serious transmission problem a car will not jerk forward or backwards while in neutral or park.

There are no codes for it to read. No check engine light or anything. And by jerking I mean my car physically jerks forward, as if I was rear-ended.

How this could happen when the vehicle is in Park is a mystery to me.

Yeah. Same here. That’s why I’m asking.

Has anyone else driven this vehicle or that can drive it and give a better description of the ’ jerking ’ ?

I also don’t see how the vehicle can move in park .

The we are back to my guess that you have a transmission problem.

I suspect purebred is on the right track in thinking transmission but you could also have a couple of problems simultaneously. Does the tachometer jump or the engine rev when this occurs? If so, your engine is surging at idle but it shouldn’t have any effect when the transmission is in park or neutral. I sympathize with your financial situation hut you need to take it to a good mechanic, one with some gray in his hair, and get a seat of the pants diagnosis.

The engine lags. Almost like it wants to die, but it never actually does. You can see the rpm drop down to about 500 when it does it. I took it to 3 different mechanics the first time, all of them reputable shops. One said motor mounts, one said low freon, the last one fixed the spark plug and coil and it was working fine until I changed the spark plugs again.

My ex has driven it, because he thought I was explaining it wrong. I realize it is not normal for a car to do that. But it does.

Car running fine,
You changed the spark plugs,
Car running poor,

Go back and see what you screwed up, you did something wrong.

I had someone who works on cars change them. It wasn’t me specifically. They own their own shop, so I’m pretty sure they knew what they were doing. Never mind.

Have you contacted them ? I don’t think I am the only one here that can’t understand what is going on with your car. You said the jerking felt like you had been rear ended and it happens in park and neutral which makes no sense at all .

It seems that a solution to your problem will need someone to actually experience the jerking in person so a better shop might be the only answer .


It jerks in park? Why are you sitting in park? To see what happens? I start car and drive.

The light dawns. Your car is misfiring badly. It’s acting like my Corolla did each time a coil was bad. You have another bad coil or possibly the car doesn’t like the brand of plugs that were installed. Or, as @It_s_Me mentioned, something went wrong with the installation. I’d expect the check engine light to come on but I understand that’s not always the case.