Rough idle AFTER carbon cleaning?

[12114]

Hey guys, so I did carbon cleaning with walnut shells but I still get the same symptom of having a rough idle for the first thirty seconds on a cold engine... Is this normal? Car is 2012 sedan btw

 

[Mark_888]

No good dead ever goes unpunished.

 

[12114]

Just saw a post on my other thread by another guy. He talked about the oil leaving the intake valves after sitting for a long time which might be causing this problem... And he's gonna try 10w40 to see if it goes away... Interesting.

 

[Gunkk]

Well if it was rough before and after the walnut shell treatment, then what the treatment cleaned up wasn't causing the problem.

Probably an injector or two that's fouled and gets slightly better after heating up. If they had the manifold off to do the walnut shell treatment, they should have pulled/tested the injectors too and/or changed plugs. Why do only 1 of the big three?

If they didn't, then throw a couple bottles of Techron in the tank and switch to a top-tier premium for a few tanks. Odds are low it will fix a really bad injector, but it's only $25 for the techron and you might get lucky.

 

[OUsig]

Get some spray seafoam and clean the throttle body.
I clean mine and even after 5 or 10k miles there is noticeable amount of carbon buildup around the plate.

 

[charliet1948]

I had the same problem, once the car warmed up idle was much better. Did a smoke test noticed smoke coming from the intake manifold gasket. Anyway replaced the 6 oval gaskets and the idle was perfect. Now the reason, when the car warmed up the seal on the gaskets were much better, not perfect just better. You can do it yourself for about $25 or have a shop do it for 250-400. I would also recommend since the intake has to come off (3.8) to access the passenger bank changing the plugs. Hope this helps

 

[2015genesisNewbie]

Hey guys, so I did carbon cleaning with walnut shells but I still get the same symptom of having a rough idle for the first thirty seconds on a cold engine... Is this normal? Car is 2012 sedan btw

I’ve been wanting to get this done in this thread just discouraged me LOL. I also have rough idle issues. How much was the one that blasting? Because of your post I don’t think it’s going to fix my idle issue but I would still want to get it done regardless. My 2015 5.0 just hit 60K

 

[2015genesisNewbie]

I had the same problem, once the car warmed up idle was much better. Did a smoke test noticed smoke coming from the intake manifold gasket. Anyway replaced the 6 oval gaskets and the idle was perfect. Now the reason, when the car warmed up the seal on the gaskets were much better, not perfect just better. You can do it yourself for about $25 or have a shop do it for 250-400. I would also recommend since the intake has to come off (3.8) to access the passenger bank changing the plugs. Hope this helps

Any knowledge if this would fix rough idle issues on a 2015 5.0?

 

[carguy75]

Any knowledge if this would fix rough idle issues on a 2015 5.0?

I have an 2015 5.0 with 76k miles on it and it idles very smooth.

The only time it had an rough idle was when it had 36k miles at the dealership(I bought it used)while using a tank of 87 octane fuel provided by the saleman, however the rough idle smoothed out with 93 octane on the following fill-up. My car has been running and idling smooth ever since with 93 octane fuel.

 

[2015genesisNewbie]

I have an 2015 5.0 with 76k miles on it and it idles very smooth.

The only time it had an rough idle was when it had 36k miles at the dealership(I bought it used)while using a tank of 87 octane fuel provided by the saleman, however the rough idle smoothed out with 93 octane on the following fill-up. My car has been running and idling smooth ever since with 93 octane fuel.

I literally spent all day yesterday looking through this forum and that seems to be the only advice for a rough idle. Use 93 octane and I’m not saying it won’t work. That’s actually what I plan on doing is switching to 93 and following up with you guys in a few weeks. However I don’t think that’s going to make a difference because I’ve been using 87 since I bought the car and never had an issue until recently. Even with 87 like you’ve mentioned several times I couldn’t even tell the car was running!

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[packettec]

I literally spent all day yesterday looking through this forum and that seems to be the only advice for a rough idle. Use 93 octane and I’m not saying it won’t work. That’s actually what I plan on doing is switching to 93 and following up with you guys in a few weeks. However I don’t think that’s going to make a difference because I’ve been using 87 since I bought the car and never had an issue until recently. Even with 87 like you’ve mentioned several times I couldn’t even tell the car was running!

There is another thread guy had all the injectors changed after trying everything else mentioned.
I suspect just clogged injectors going to try a red neck cleaning process as soon as I get some time, want to check fuel pressures first.

 

[2015genesisNewbie]

There is another thread guy had all the injectors changed after trying everything else mentioned.
I suspect just clogged injectors going to try a red neck cleaning process as soon as I get some time, want to check fuel pressures first.

I thought GDI wasn’t as susceptible to clogged injectors since they are spraying at such high pressures? Kind of like my sprinkler in the backyard always gets clogged up with calcium deposits or whatever is in the water but my pressure washer nozzle never gets clogged up

 

[packettec]

I thought GDI wasn’t as susceptible to clogged injectors since they are spraying at such high pressures? Kind of like my sprinkler in the backyard always gets clogged up with calcium deposits or whatever is in the water but my pressure washer nozzle never gets clogged up

From memory I think they tried every other likely possibility coils plugs even one injector took it back and he said they changed all injectors except the one previously changed and problem was resolved.

I remember way back reading another thread on fuel pump failures thats why I want to check the pressures before wasting time on cleaning when it maybe related to low fuel pressure at different times.
I'm going to see if I can mount my manual pressure gauge to it for a few days see what I'm getting at different times. It's started getting hot here and have bigger problem with no AC.

 

[2015genesisNewbie]

Just added 2 bottles of Techron. 1 black and 1 grey because I don’t know the difference between the 2. I know that won’t do shit for the intake valves if that’s my issue but whatever. Added both bottles at the same time into an almost empty tank (3/16). I know you’re supposed to fill it up right after but I didn’t. Now it’s almost completely empty (1/16) and will fill with 93 tomorrow. Burn through that and fill with 93 again and let y’all know if it made any difference.

 

[2015genesisNewbie]

Also I remember reading on here that someone was buying Techron on sale for like $9/ bottle. But when I just bought them at Walmart both black and grey bottles (10oz and 12oz) are a little less than $5/ bottle…

 

[Bibi]

Also I remember reading on here that someone was buying Techron on sale for like $9/ bottle. But when I just bought them at Walmart both black and grey bottles (10oz and 12oz) are a little less than $5/ bottle…

So what’s the verdict? Did the bottles and better gas fix your issue?

 

[2015genesisNewbie]

So what’s the verdict? Did the bottles and better gas fix your issue?

Nope but I’m still on my first tank of 93. I should also mention ALL 8 of my fuel injectors as well as my intake manifold gasket were replaced under warranty on 6/17/20 at 54k miles so it’s definitely not the injectors. At the time my car was running fine but the check engine light came on and I took it to the dealership and that was the decision they made I honestly couldn’t say whether or not the rough idle existed before then or not. I honestly can’t remember. At this point I’m thinking maybe the MAP sensor, excessive carbon build up on intake valves, throttle position sensor or worn cams??? But I don’t know how any of that makes sense to cause rough idle ON COLD START ONLY. After I drive it for 5-10min the idle is smooth as silk at 500rpm.

 

[Bibi]

Nope but I’m still on my first tank of 93. I should also mention ALL 8 of my fuel injectors as well as my intake manifold gasket were replaced under warranty on 6/17/20 at 54k miles so it’s definitely not the injectors. At the time my car was running fine but the check engine light came on and I took it to the dealership and that was the decision they made I honestly couldn’t say whether or not the rough idle existed before then or not. I honestly can’t remember. At this point I’m thinking maybe the MAP sensor, excessive carbon build up on intake valves, throttle position sensor or worn cams??? But I don’t know how any of that makes sense to cause rough idle ON COLD START ONLY. After I drive it for 5-10min the idle is smooth as silk at 500rpm.

Is your vehicle still within warranty? If it is, I would totally have them take care of that issue.
I REALLY hope your issue goes away.

 

[2015genesisNewbie]

Is your vehicle still within warranty? If it is, I would totally have them take care of that issue.
I REALLY hope your issue goes away.

Not within the 5yr/60k but still within the 10yr/100k powertrain… I’ll let you know!

 

[Gunkk]

Nope but I’m still on my first tank of 93. I should also mention ALL 8 of my fuel injectors as well as my intake manifold gasket were replaced under warranty on 6/17/20 at 54k miles so it’s definitely not the injectors. At the time my car was running fine but the check engine light came on and I took it to the dealership and that was the decision they made I honestly couldn’t say whether or not the rough idle existed before then or not. I honestly can’t remember. At this point I’m thinking maybe the MAP sensor, excessive carbon build up on intake valves, throttle position sensor or worn cams??? But I don’t know how any of that makes sense to cause rough idle ON COLD START ONLY. After I drive it for 5-10min the idle is smooth as silk at 500rpm.

This tells me it's happening only on cold start open loop mode, and the ECU can compensate when running closed loop with the O2 sensor inputs. So the telltale will be the ST and LT fuel trims.

Get a cheap OBD2 reader and torque app and watch your fuel trims. If they're way positive, you probably have an air leak or a bad MAP/MAF sensor. If they're way negative, maybe a sticky throttle plate or bad MAP/MAF sensor, totally clogged air filter (unlikely); or perhaps one or more sticky (open) injectors, but this is less likely with new replacements.
Very easy to screw up modern cars when pulling the intake off, with all the old plastic fiddly bits and gaskets. Could also be compression/plugs but you'd usually see a misfire code if really bad. Our cars seem to be moderately tolerant of cold start open loop "rough" idle short of complete misfire.

Do you know what the CEL code was before you took it in?