My Civic LX engine D16Y7 has 65K miles so it is time to replace the spark plugs.
I looked up in the owner's manual and the NGK replacement part is ZFR5F-11. I bought the iridium ones ZFR5FIX-11.
When I removed the old ones, to my surprise they were ZFR6F-11.
Note that this car has only been serviced at a Honda dealer, and as far as I know the spark plugs have never been replaced.
I installed the spark plugs anyway and the car has low rpm at idle.
I disconnected the battery to reset the computer with no result.
I have not found any recommendation to use ZFR6F-11 instead of ZFR5F-11, so does anybody know why Honda would install at the factory one type and recommend another as replacement in the manual?
Thank you

Yes, the ZFR6F-11 are for use in warmer climates; i.e. they are a colder-running plug. Since I live in Texas, I use colder-running NGK plugs in my Civic. If you look in your owner's manual, and/or on the sticker under the hood, you'll likely see what Honda did is fine.