[Gmdykfuiygh66476]

This is mainly for Darth-Apple but I'll leave it open for discussion as well... I'm also not much of a car guy so I'm not really sure how all this works.

Ever since I bought my 2012 Kia Rio 5 the thing has had minor issues with a slight engine rattle and losing power in low RPM ranges, but I learned to live with it and it was never bothersome. However, over the past few months or so the problem has been steadily getting worse, now it has reached the point of an incessant and loud spark knocking on acceleration and under load. My mileage has also seemed to drop significantly.

After doing some reading around I found out that many others also have the same problems, and after taking it to the dealer have been told there is no issue. Some people have said that using premium gas has helped (but I really couldn't be bothered to spend the extra money). I'm beginning to think it's just a problem I'll have to live with as it seems that these particular engines do this a lot (even though there's nothing mechanically wrong with them). 

Either way, I just wanted to get a little bit of input and maybe advice/suggestions. Given this and other experiences with this car I've already decided not to bother with another Kia anytime soon

[Darth-Apple]

Loud "spark knocking" under load? Hmm... not sure I've ever really heard of that. Does it seem to be rough and bumpy at low RPMs or when under throttle, but smoother when coasting at moderate RPMs without the foot on the gas pedal? How long has it been doing this?

I'm doubtful that premium gas will really be a solution because even on vehicles that specifically require premium gas (including mine, for example), the engine has something called a knock sensor that can make small adjustments to prevent knocking even if the wrong fuel is put in. So the car should be able to avoid knocking no matter what fuel is used. Higher octane gas, however, is, by design, more resistant to knocking, which is why many people choose to use it in older vehicles where carbon buildup in the engines might make them a little more susceptible to knock.

If premium gas solves the issue, the culprit is probably a lot of carbon buildup within the engine (though this is uncommon with newer vehicles with lower miles). In that case, a good can of sea foam will probably help solve that problem. Otherwise, without really knowing what it sounds like, do you know if the spark plugs and all of that have been changed recently? An old plug can sometimes fail to spark or spark inconsistently, resulting in a ride that is not nearly as smooth as ideal. They are supposed to be changed every 30K miles in Rio's, if I remember correctly. In my car they are every 100K miles, but I actually put different plugs in on purpose because they are (supposedly) a slight bit better on the performance edge, so I change mine every 20-30K miles. It makes a big difference every time.

[Gmdykfuiygh66476]

I may be using the wrong term but basically it's fuel not igniting properly resulting in the loud rattle and slight loss of power. Haven't had an engine light come on or any major power loss like a misfire though (yet). It sometimes idles rough and at low RPMs but not consistently.

Unless it was done by the dealer or previous owner (probably not) the plugs haven't been replaced. I didn't find anything in the manual about plugs specifically but it does recommend a "tune-up" every 100k miles or 7 years. 

Really I'm close to getting a new vehicle so I won't worry about it much. In the meantime I'll just use premium fuel and see what happens. If not I'll just take it somewhere (again I'm not really a car person)

[Thomas]

Replace the spark plugs. It's probably as easy as that. When you have ignition issues, the safest bet is typically the spark plugs. I wouldn't bother with premium fuel. Premium is actually harder to ignite than regular, and your engine won't run any better with it.