Brown spark plugs and an intermittent rough idle
 

My most recent project that I just completed, on occasions I get a rough idle. I've tried several different gas stations thinking that that could be were the problem comes from, but no matter which one I use, I get an intermittent rough idle. Does not do it all the time, but still concerned me. So I read here and other places to use only the AC Delco spark plugs. When I purchased the car back in Sept of 2022, the first thing I did was put in E3 spark plugs. I did this to every car I have purchased over the past 10 years or so. Not once have I had any problems. When I changed them out for the 14-103 Delcos a few weeks back, the E3s that I pulled out were brown, like a regular brown, not burnt or anything weird, just brown. Installing the AC Delcos didn't change the issue.Now I did get the new plugs off of eBay motors for a substantial less price than the parts store. I did it thinking “ I sure hope they’re right!!” Well when they came in they were in a generic box, but the plugs inside said AC Delco and the14-103 part number. So I was like cool. So I installed them without thinking twice about it. The idle issue is still there. My next project is to pull one and see if they come out like the E3s, brown. If they do, what in the heck could be the reason why they are turning brown??? I’m not burning oil, did have a leak at n the valve cover last summer but fixed it. There was oil in the spark plug pie then, when I did the gasket. But when I did the plugs, no oil in the pipe.Im hoping that someone else has run into this or has better thinking capabilities that can come up with some possible reason as to why this and that is happening.I’ll pull the plugs and take pictures and show what I find.Thank you all and have a good day.

Could be a dirty throttle body, dirty MAF sensor.
to clarify you installed AC Delco 41-103 iridium plugs?
you did not attempt to gap them? The whisker tends to break off if you do.
EBay in a generic package? You get what you pay for.

how is the air filter?

Did you clean the throttle body? Any CEL?

I hate to do this but I may have to start from the very beginning with the acquisition of Ameilia.
I purchased her used from a local car lot that I have purchased several cars from back in September of 2022
The first thing I do when getting a "new" car is
upgrade all the lighting to LED lights (headlights, brakes lights, turn signals, license plate lights)
Changed out the spark plugs to E3 plugs, I've done it in all my cars for over the past ten years and have had no adverse
issues
Checked the air filter, it was a basic paper filter and was brand new, no change, the only down side was that the intake
hose was deteriorated. This is one thing I know I need to change but am having difficulties finding a decent cold air
Intake for Ameilia (suggestions recommended)
Other than that, that is all I had to do the first year I got her.
Then in the summer of 2023 I had to change the battery and starter.
After that the CEL for the knock sensor came on. So I changed the sensor, no more DTC.
About 5 months later she began to have issue starting. Come to find out that the nut holding the starter wires had come loose and had begun to arc. Figured this out and replaced the starter again. Made sure that everything was tightened down and that there shouldn't be my more issue with that.
Summer of 2024 the exhaust clamp broke at the junction between the convertor and collector. Replace CaT back, no more issues.
Summer of 2025 the DTC for the knock sensor came back. Had it looked at and the oil sending unit was leaking directly onto it being the possible culprit.
Took a bit of time and money but finally replaced it (oil sending unit) and no more knock sensor DTC
Now it's just the P0128 coolant temp DTC

During this time the rough idle began, tried several different gas stations to see if it was that, tried 87, 89, and 93 octane to see if that would help. Ran injector cleaner through several times in between fill ups, not every fill up. This helps for a little while then the rough idle come back
Now, the rough idle isn't a detrimental kind of idle. At a red light it just kind on boggs down a bit then goes back to normal. It's not affecting performance, that I can tell, it's just a nuisance that I'd like to get rid of.
Could this just be the it has 260,000 miles and it's just going to be that way
Could it be timing,
Or could it be something worse

This is the entire history of Amelia. She has been a great car. I do oil changes every 5000-7500 mile. Most of my driving is "city" driving, meaning my average speed is about 45mph. I use Mobile One High Mileage 5W30 and a Mobile One filter.

Reading this I hope I do not overwhelm those reading this and hope it all makes sense. If there is something else I can be doing or habits that I can change to keep her running, I'd like to get 300,000+ out of her, that'd be great.

I look forward to the comments and suggestions. Thank you in advance.

Wrong plugs! AC Delco 41-103 Iridium plugs are the plugs the engine is designed for!
P0128? Replace the thermostat with an AC Delco 131-158 180 F . Yes they are pricey but they work for a long time!

if there is still a rough idle , clean the throttle body and MAF sensor, check the timing chain and front guide!

You can just look at the timing chain; any slack between the sprockets is bad.

My apologies, I knew there was something I was forgetting.

I replaced the plugs but 4k ago with the 41-103 plugs. On the original install at 180,000 when I got her in 2022 I put in the E3's. However, after reading many many threads on here and other forums, I did replace them with the 41-103's and no, I did not attempt to gap them. Amelia currently has approximately 265,000. Other than the above items, I've not had any serious issues with her.
As far as the thermostat, I will do the sensor first since it is an intermittent issue, wait a few weeks and just before summer, do a complete purge and re service of the coolant system and a new thermostat.
I cleaned the throttle body about 5k ago as well, before the plugs. I have also run fuel treatment through the system. These along with some 93 octane help for a bit, but right now, thanks to other issues, 93 is upwards of $4/gallon.
Reading through my original post and here, I believe I have covered everything.

Thank you for your patience in my endeavors, and I look forward to the replies.

Thanks, Krazy Fokcer

Of course P0128 is intermittent; it depends on the water temperature when the engine is started. I.E.: the time from 32F to 180F is longer than 120F to 180F. It also senses the running temp, if it runs less than 179F the code will set.
Running cold can lead to carbon build up and poor ignition of fuel in the cylinders. Cooler is not better!
93 octane is a waste of your money unless you have an SS with a tune. It has the same detergents in it as 86 Octane.
41-103 plugs are good for at least 100,000 miles, Most get much more.

Luckily RockAuto had both the thermostat and the sensor in stock and should arrive by Thursday. So my next project will be next weekend. I am looking forward to this one. I've also got some cosmetic upgrades coming too. I'll make an update on that in the proper forum later on. But it's killer..... Thanks for all the help. KrazyFoker

If you can find one, Airaid 203-195 or 200-195. The 200 uses their oiled synthetic filter, while the 203 uses a oil-free synthetic filter. Both are considered lifetime filters, & it makes cleaning / changing the air filter so much easier!

Here it is when it was installed in my 2010 HHR LT, though it's now sitting in my 2010 HHR LS:
https://cimg1.ibsrv.net/gimg/www.che...b2cfec7bc2.jpg

Now I take off one hose clamp, pull off the filter and wash it out every 6 months, let it dry, and reinstall. I did have to bend part of the housing though, as the left side used to sit directly over top of the coolant reservoir port, as can be seen here:
https://cimg6.ibsrv.net/gimg/www.che...bb6d045324.jpg