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It's not really a problem, but more of a question so I'll post this here. Sorry if I'm doing wrong.

So I finally changed my fourth sparkplug after delaying it for about a month now. (If you're wondering why only one plug?... I broke the one supposed to be in there while tightening)
I've been running the car with 3 new plugs with one old plug, and it sometimes had weird vibration (bop.... bop... bop... almost a 0.5 sec interval) in the engine area(I think) when I was stopped and I thought if ECU is making the old plug misfiring or something because of mixed plugs.
I don't have OBD reader to confirm that but I just went by since the car was running fine.

but after changing this last one... car feels more powerful now. Don't have to press gas pedal as much as before to reach same speed now.
The question I have is, though, is the car's ECU actually adapting to sparkplugs being changed? Maybe ECU now knows that all the plugs are sparking strong that maybe making it run more powerful?
If that's true... it's truly wonderful what a car knows/does.

P.S.
Here are pics of 4 (well, 4 and a half because a mechanic needed to break one's half to make a plug remover) old sparkplugs and one that was broken, if anyone is interested.
I tried to remove the 3 plugs to see how they looked after a month but they were SUPER tight so I will just leave them be... don't wanna repeat the same thing again.

 
Rep Power: 126

Your car was most likely misfiring in the cylinder with the old plug. With the lack of power it almost sounds like you were running on 3 cylinders

 
Rep Power: 119

Normally just leaving a old plug in is not the issue, but if you left a “bad” plug in it would possibly explain your observations.

Yea those spark gaps sure seem well beyond spec on the old plugs so I am guessing it was “bad”.

If there is a 100% lack of fire in a plug the ECU typically can figure it out and send a misfire code for the cylinder.
If the plug is late / intermittent to fire then the ECU really can’t be sure what’s going on.
So it starts to address fuel trim to stabilize the input it’s getting from the upstream O2 sensor which will affect drive ability.

 
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Yikes, if it was misfiring and was running on 3 cylinders.. would that damaged my engine?

The power difference is like pressing 1/5 of gas now, compared to 1/4 before to reach 60-70 kph in 7 seconds on flat surface

 
Rep Power: 126

It shouldn't unless the misfire caused you to run super lean, but if it runs well now, then I don't see why you'd have any issues related to that.

 
Rep Power: 244

Misfires can cause damage to the cat.

 
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Damn hope I wasn't too late...

 
Rep Power: 223

Probably fine if it was just a month

 
Rep Power: 244

I'm sure it's fine like Colin said. I would't worry too much about it. Just drive it and enjoy the new power.

Keep an on that temp gauge though.

 
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It kinda overheated last night when I was heading to work, tried securing rad cap again and I think it'd good.

Now I'm trying to figure out if my head gasket's blown.. a new thread here: https://www.civicforums.com/forums/3...n-stopped.html