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Car stuttering and lacking power

2007 Hyundai Accent

For the last couple of months my car has been misfiring, rough idle, weak acceleration, etc.

To date (since around august) I replaced my spark plugs (car ran great after that for a bit) then in the last month or so it started to misfire somewhat frequently (when I say that I mean the CEL turned on and flashing). Plugged in my code reader and got a misfire in cylinder 4. So for that cylinder we; replaced the boot, the ignition coil, and now the fuel injector (mechanic said it wasn’t consistent with dispensing fuel, so it was replaced, along with every other injector being cleaned and sea foam added to the gas tank).

Just got the car back yesterday and driving to work it has familiar symptoms of before. When accelerating from a stop it kind of stutters and does one hard shake, that happens from around 30-35mph. And then trying to go over 40 it starts to shake and stutter unless I accelerate it more over to around 55-60. I can tell when it’s going to happen because I’ll hear the car reving, then it’ll stop and start to shake hard and have bad power. Weirdly enough, when I turn overdrive off, the problem stops and the car accelerates well.

I drive about 25 minutes to work (I go on a highway to another town) and this only seems to happen after I’ve gone highway speeds for awhile and and into the town where my job is and go in-town speeds.

So guys, anything else you think can stop this bad power and shaking issue? My oil still has about 1.5k miles left, spark plugs are new, cylinder 4 has had pretty much everything replaced in it. No misfires yet, no codes yet.

Mass airflow sensor? MAP sensor? Transmission issues? Should I replace all my coils instead of the one? I’m lost.

I’m thinking torque converter lock out problems. The missfire was legitimate but unrelated.

Great description of symptoms but no mention of the mileage on the car and the actual P code you read. You didn’t tell us, I’ll assume a P0304.

New plugs made it run well for a while, hmmm. Does the engine used oil between changes? How much? Have you done a compression test on the engine?

Its an 07 so it has, on average, 165,000 to 180,000 miles. May have more, you didn’t tell us. If the car is using oil, that may be a partial cause of your misfire and the shaking you feel. When you changed the plugs, did the electrode end look black and oily? Or tan colored and dry?

Sorry I left out stuff it was a lot. Car only has 83k miles, oil was changed at 81. I didn’t do the repairs, mechanic did. He said the plugs were pretty black. Also all of my boots were changed, not just the one in cylinder 4 where my sensor read the misfire (it was the code you described). I’m sorry but I’m not sure what you mean by using oil. My oil level is fine, along with my transmission fluid level. However I can recheck them later. I have not done an engine compression test.

If that were the case, what are my options?

If that is the case, it can be properly diagnosed by a good mechanic or a reputable transmission shop. It could be something as simple as a solenoid, but diagnosis is important.

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“Using oil” means you checking the oil level periodically between oil changes and adding as needed. If you check the level after an oil change an it shows at the full mark you are good. If you check the dipstick 1000 miles later and the level has dropped to the “add” line and you add a half a quart of oil to bring it back to full, your oil use is 1 quart in 2000 miles. Perfectly fine.

Since you have 1500 miles to go before the next change, go check it right now. Add oil, if needed (and I think it WILL need oil) and take the # of miles since your last change and divide it by the oil used.

Sure sounds like it is using oil or a lot of excess fuel - but that would toss a second code. A car this old with so few miles likely means the previous owner didn’t change the oil often enough and it may have sludge built up in the engine. What is the car’s history, if you know?

Begs the question… why are you going on the internet to get answers rather than ask your mechanic or let him find and fix the problem?

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There you go , being logical .


ooops, Sorry 'bout that! :laughing:


If the compression test checks out ok, and the ignition system tests ok using hyundai scan tool or preferably lab o’scope, fuel trim test is what I’d do next. When you have a misfire in only one cyldinere the common way to diagnose is to swap parts between that cylinder and one that works and see if the problem goes to the other cylinder or not. spark plugs, coils, ignition wires, boots, injectors etc are common parts to swap.

How’s the battery?

Thought I’d update y’all. Decided to change all of my coil packs. Think I found the culprit lol. Car is good now.

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