Rough idle

[unlock42]

With only 4,200 miles on it? I've barely had my first oil change.

What elevation are you at? There could be some variables at play here... I'd try using Premium and see if smooths out a bit.

 

[carguy75]

With only 4,200 miles on it? I've barely had my first oil change.

Not carbon build up. You engine is too new to have an carbon build-up issue. However, your rough idle is mostly a cause of using 87 octane in your engine which cause your engine to run rough by retarding the timing to overcome the high compression. The quality of gas plays a part as well since gas can lose it energy as it ages; so 87 octane can become 86 octane or less depending on the gas station you use and its gas quality.

87 octane also produces more carbon in the engine due to having less detergent which keeps the fuel injectors and piston tops clean. Over time the carbon will foul the injectors and build-up on top of the pistons which could cause your engine to run even rougher than it does now as the miles increase. Quality premium gas will reduce the carbon build-up and allow your engine to make the most power under full compression by not retarding the timing.

However, Hyundai does market your 3.8 to run on 87 octance yet it has over 11:1 compression. The engine would run better on premium I bet like the 5.0 engine.

 

[Kraig Wilkinson]

My '19 3.8 idles kinda rough, too - but it only has 4,200 miles on it. Think it'll get better?

I would try a couple bottles of techtron TinsleyC. It will most likely help out your rough idle.

 

[lopedogg]

Using non ethanol fuel in small engines is key. Ethanol is what eats up the rubber tubing. I bought a new weed eater about five years ago and the guy selling it told me it'll last twice as long if I just avoid ethanol. So I buy the red cans of pre-mixed fuel at Lowe's or Home Depot and it's also a lot easier than mixing my own.

Good call, A little off topic but for my small, 50:1 2-Strokes, I try to run 60/40 AvGas and regular/premium. The engines seem to run smoother and you don't have to worry about your gas going bad after sitting all winter.

 

[TinsleyC]

I would try a couple bottles of techtron TinsleyC. It will most likely help out your rough idle.

I'm just not sure there's anything to clean with only 4,200 miles on my car. What would the Techron clean out, or do?

I use the stuff on my cars, I actually have five 20oz bottles in the garage right now, got a good sale on them. My mother in law's 4Runner with 105k was running rough and one bottle got it cleared up. Then she replaced the spark plugs and it made a big difference.

 

[TinsleyC]

What elevation are you at? There could be some variables at play here... I'd try using Premium and see if smooths out a bit.

I'm in Dallas, so we're like 700 feet. Car was designed and tuned on 87 so just not sure why I would need a premium fuel. Others have said the idle smooths out after the engine aged a bit, would that not apply to the 3.8 as well?

It's just a slight and occasional roughness, nothing major. But I can try a tank of premium to see if it makes a difference. I always use a TT fuel.

 

[Kraig Wilkinson]

I'm in Dallas, so we're like 700 feet. Car was designed and tuned on 87 so just not sure why I would need a premium fuel. Others have said the idle smooths out after the engine aged a bit, would that not apply to the 3.8 as well?

It's just a slight and occasional roughness, nothing major. But I can try a tank of premium to see if it makes a difference. I always use a TT fuel.

With the tip of injector in combustion chamber , it is subject to all of the chaos related to a combustion chamber. Heat, gases , fast temp changes, etc. It only takes a very, very little carbon/ dirt to foul up the spray pattern of injector. Try it out and take her for a high revving drive.

 

[unlock42]

mother

I'd definitely try using premium and add techron on top of it even to see if that helps.

BTW how much were you able to buy the pack of 20oz techrons for? The cheapest I've been able to order them was ~$9 a bottle for the 20oz.

With the tip of injector in combustion chamber , it is subject to all of the chaos related to a combustion chamber. Heat, gases , fast temp changes, etc. It only takes a very, very little carbon/ dirt to foul up the spray pattern of injector. Try it out and take her for a high revving drive.

Very true. Let alone GDI's are more prone to get dirtier faster by nature. It's amazing what just a bottle of techron can do.

 

[Kraig Wilkinson]

I'd definitely try using premium and add techron on top of it even to see if that helps.

BTW how much were you able to buy the pack of 20oz techrons for? The cheapest I've been able to order them was ~$9 a bottle for the 20oz.



Very true. Let alone GDI's are more prone to get dirtier faster by nature. It's amazing what just a bottle of techron can do.

Totally agree!

 

[TinsleyC]

My last purchase of Techron was four 20oz bottles buy one, get one free, $30.29 for four - so about $7.57 after tax. Advance Auto Parts.

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[surprisinguy]

Advance Auto Parts

Dont forget to order online, then apply a "Retailmenot" discount code -%25 when ever you buy there.

 

[DV_hat]

This is interesting - I found that my 3.8 has a rough idle when the AC is on. It is pretty smooth otherwise but it's not fully quiet, I can still tell the engine is running when I'm at a light. Would premium gas help with this problem?

BTW I've been told that the ECU takes time to adjust to the new octane, did you guys feel any knocking when you first switch octanes?

 

[carguy75]

This is interesting - I found that my 3.8 has a rough idle when the AC is on. It is pretty smooth otherwise but it's not fully quiet, I can still tell the engine is running when I'm at a light. Would premium gas help with this problem?

BTW I've been told that the ECU takes time to adjust to the new octane, did you guys feel any knocking when you first switch octanes?

I never noticed any knocking in the engine when my 5.0 V8 ran 87 octane, it only ran more sluggish and idling rougher than it does now with 93 octane.

My mpg was not as high as it is now, however I can not remember exactly what it averaged. It was in the high teens(18 mpg or 19 mpg) with 87 octane with my style of driving. I now average about 21 or 22 mpg with my mixed driving(mostly city with some highway) commutes with 93 octane, more(24mpg-26mpg ) if I drive the speed limit without accelerating like a race-car driver.

Premium gas helped my 5.0 V8 overall performance, however I do not know if the same will happen with the 3.8 V6.

 

[cudaus1]

As the pistons build up gunk it often decreases the overall volume, thus increasing the compression every so lightly; to the point where using higher octane fuel makes it run smoother.

Remember, higher octane fuel doesn't mean that it is a better gas, it just means that it takes longer to combust for higher compression engines.

It's not uncommon for higher octane gas to make engines run smoother that has built up gunk.



I used to be a hard core Shell fan and at one point and one of my cars only sipped on Shell until I sold it. The claims by shell are simply "claims." No one really knows, because petrol companies are hiding behind the whole proprietary nonsense and not being transparent these days.

I do think that Shell despite their claims remain the King of the Petrol jungle hands down, but over the years and due to the 4% cash back at Costco, I make my own Shell by just adding Techron full system additive every ~3K miles or so lol.

All the raw petrol is the same across the board, with the difference only being the additives each company adds to it. So instead of paying upwards of 50 cents more per gallon, if you buy a bulk of 20oz Techron for ~$9 a bottle (w/ 5% Amazon cash back in my case), you'd be on par with breaking even after only 18 gallons of filling up on Shell, which is pretty much one fill up.

I've always looked at it two ways.

If you use Shell and IF it really is potent with its claims then you're constantly cleaning and maintaining that, which is good.

If you use the Costco + Techron every ~3K method like I am, then maybe it's not cleaning as much consistently, but when it does clean on that full tank w/ 20oz of Techron... is having that concentration to 'shock' clean the build up as effective? Who knows...

If you want to go all out, use Techron every few thousand miles on top of Shell to have Pearl Fuel.



Indeed. That's what I normally do. Depending on the season I'll go through about 3-4 Techron treatments before an oil change. Sometimes my oil change internals overlap with the fuel treatment... I keep it pretty ball park estimate...

About that Italian treatment... usually on the tank before my oil change I'll take it for a good spin to try and burn off all the gunk.

I just buy Chevron gas. The Techron is already in it at the pump.