Rough Idle after spark plug change

[Inv4drZm]

I decided to change my own spark plugs today at 120k miles as preventative maintenance. 8 Denso Iridium SK20R11. After doing this, I started up and listened. Nothing abnormal. Drove a mile and on idle it ran really rough and the exhaust was "puttering". I pulled all the plugs again, making sure to clean the coils or boots as much as possible. Noticed a cracked spark plug (I think) shown below. Maybe I overtightened it, or dropped it, or it came that way?



Wiped down these thingies-


Once I replaced the cracked one (Amazon sent me a few extra!) and cleaned all the coils (or whatever they're called) And double checked I didn't break a wire or not click a connector all the way. Idle was fine for a couple minutes. I drove it a mile listening closely and when I parked it, I realized it still wasn't 100%. You could barely hear it and feel it running like it couldn't decide which RPM to run at. The exhaust still sputtered.


Do you have to check gaps on every spark plug? I assumed these were already correct.

I didn't use any anti seize and made sure to just snug them up.

I'm at a loss here. What did I do wrong?

 

[Morphyne]

Could they be the wrong plugs?

 

[wcjeep]

Never assume the factory gap is correct. Always double check. I have found a few that were off. Did you use dielectric grease? I'm not familiar with Toyota engines. Are those the factory recommended plugs? I stopped using fancy plugs for just because. After double checking everything, try unplugging the battery for a few minutes. Allow the computer to relearn new parameters.

 

[Morphyne]

And if they are the right plugs then no you don't have to gap them

 

[Inv4drZm]

Could they be the wrong plugs?

I've seen these plugs recommended on here a couple times as the Toyota recommended replacements. The little boxes they came in were all the same #s but I didn't actually double check all the plugs themselves.

Are those the factory recommended plugs? I stopped using fancy plugs for just because. After double checking everything, try unplugging the battery for a few minutes. Allow the computer to relearn new parameters.

I might unplug the battery, that's a good idea.

It could be I'm just paranoid. I drove around some more and stopped periodically and had rock solid RPM in Drive. Park though varied a bit but this could be normal and it never had any knocking or rumbling like before the cracked plug was changed. I would like to think it is fixed now, but I will continue to monitor.

 

[dkyleb]

I ALWAYS check every plug that goes into whatever I'm working on. They all come pre gapped now adays, but mistakes happen. Checking them has saved me once, and now I'll always do it.

 

[Gdmeadors]

Those appear to be the correct plugs. They do not require gapping per Toyota. There is sticker on the driver's side of the engine block on my V8 that warns against gapping them. Your engine may be relearning the idle speed, etc. if you disconnected the battery.

 

[eugnandez]

They all come pre gapped now adays, but mistakes happen.

 

[Brokeazzlos]

Looks like the coil is arching. I would get a new boot or coil

 

[rick1987]

And it might not be your case, but for people who search.

Whenever you disconnect your battery, at least for my 4runner, it idles terrible!

The first time I ran into this was when I installed a remote start. The truck was barely idling. I freeked out and was tearing things apart looking for anything that would effect it from running. (Tach wire, ect)

Drove it home and it would shake at the light. I seriously thought I blew a head gasket from starting and shutting it off so many times during the remote start install.

I got home and it was still shaking, it drove fine on the highway but just sitting it was bad. I was so mad I began to try and stall it. AC on putting it into gear, turning all my accessories on and turning the wheel back and forth. It got to the point where it almost stalled but saved itself and idled perfectly.

 

[DisguisedRope]

And if they are the right plugs then no you don't have to gap them

Those appear to be the correct plugs. They do not require gapping per Toyota. There is sticker on the driver's side of the engine block on my V8 that warns against gapping them. Your engine may be relearning the idle speed, etc. if you disconnected the battery.

You should always CHECK the gap on new plugs, but with the fancy iridium/platinum/unobtanium plugs you can't CHANGE the gap as the electrode can break/bend.

 

[Morphyne]

You should always CHECK the gap on new plugs, but with the fancy iridium/platinum/unobtanium plugs you can't CHANGE the gap as the electrode can break/bend.

True. A manufacturing error will ruin your whole day.

 

[m85476585]

I haven't done any engine work or disconnected the battery recently, but I think I'm having a similar idle problem with my V8.

When it's cold (between 32-50, mostly) it idles rough like one cylinder is noisy. Usually it's at one specific speed, which might be 600-1100 RPM depending on the day (but not depending on the temperature). At the engine warms up it's better but still not 100%, just like you described. It's very subtle once it starts to warm up. When I'm driving it's perfectly fine at long as the RPMs are above 1500. If I'm driving in a parking lot or neighborhood and the engine is still cold I might hear it.

Based on some research it could be piston slap. I don't think there's really anything you can do about it if that's the case, and apparently it won't hurt anything. But it sounds bad, so I'm paranoid that something else is wrong and it's going to do some damage or something.

I can't really hear it under the hood because there's too much other nose from fans and spinning stuff and clicking stuff. It's noticeable in the car if I'm parked or driving slowly.

I don't remember it doing this the first winter after I first bought the truck, but this has been going on for about a year now, I think, mostly in the colder months. I bought it used 1.5 years ago. I've changed the oil a couple times with Mobil 1 synthetic. I haven't done spark plugs yet because I only have 92,000 miles.

Sorry to hijack the thread, but OP's issue sounds similar to what I'm hearing. So if it comes back after replacing the cracked plug it might be something else.