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Accelerating from a stop last night, my 2002 Civic LX lost all power and roughly stalled, with the Check Engine and Battery lights coming on. I had to push it off the street, but 10 minutes later it started back up and ran fine, Check Engine light still on. Today they tell me it threw the P1298 code, which it also did in 2018. I remember it losing some power under acceleration in 2018, but that was a one-time thing, and it's been fine up until last night. Does it seem likely that replacing the ELD will solve my problem?

 
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ELD is one of the common issues on this generation, so we would recommend doing so

 
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Already done. Hope it fixes it for good. The intermittent nature of the problem seems to point to the service bulletin I found, which mentions a "faulty solder joint" in the ELD.

 
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OK, so I replaced the ELD almost four months ago. My gas mileage has improved from 23-25 MPG to 25-28 MPG. I've always monitored this, and I can't remember ever getting 28 MPG, well, 27.8 to be more precise. Could replacing the ELD have improved gas mileage?

Also, I've recently noticed my interior lights and headlights dimming when I accelerate and brightening back up when I left off the gas. It's very noticeable driving in my subdivision at 25-30 MPH. The car has also been sluggish to start the last several weeks. The first start when it's cold goes easily, but then when I'm out and about, doing errands and such, subsequent starts can roll over for several seconds. Yesterday, the check engine light came on, and while the car did start, there seemed to be less than normal acceleration, so I stopped it and parked for a few minutes. I started again, and it ran normally. I took it to O'Reilly, and they checked battery, starter, and alternator but found nothing wrong. I went ahead and replaced the 2.5 y/o Walmart battery anyway with one of theirs. The car is back to starting normally, and the light dimming is no more. Unfortunately, I didn't have them read the code before replacing the battery. I've read in various places that this dimming is "normal", and the battery isn't used while the car is running, but my experience seems to conflict with this. Can anyone ELI5 to me?

 
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That's the purpose of the eld, varies the alternator output to achieve the best fuel mileage

 
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Awesome.

 
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I would be surprised if fixing the ELD made that much of a difference to fuel economy. I don't remember ever getting less than ~34 mpg when my Civic was stock, I even had the ELD go bad at one point.

 
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This 2002 LX is rated at 26 city, 34 highway, and my driving is mostly city. It's been a long time since it did 28 MPG!

Anyone have thoughts on my second paragraph about the battery?

 
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The eld will occasionally stop the alternator output and use only the battery with the car running