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Hi there! I just recently bought a 2003 civic si and after about 2-3 weeks of driving around town, I've recently noticed a strange idle issue.

Whenever I tap the throttle or slow down to a stop, the rpms will sit at ~1500 for 3-4 seconds before returning to normal idle. I was wondering if anyone has had this issue before and if somebody could give me a few pointers on how to go about fixing it, as I have done some searching around and haven't really found any definite answers.

Any ideas would be helpful!

 
Rep Power: 132

First thing I would suggest is to clean your throttle body/plate in case it is sticking from carbon buildup. Next would be cleaning the IACV. No CEL on with a code right?

 
Rep Power: 0

There is no CEL. This actually started about a couple days after I had changed my spark plugs. I got the exact same plugs that were in the car previously, and had gaped and torqued them to spec. A CEL did come on, but the car drove and sounded perfectly fine. So I took the negative battery cable off for 10 mins and reset it, and the light hasn't come back since. Since I did the reset, would it be possible that I might have to do an idle relearn?

I'll take a look and clean the throttle body/plate and the IACV once I get a chance.

 
Rep Power: 517

Absolutely. Every time the battery is disconnected.....and you may need to disconnect the battery again before you begin the learn process.

 
Rep Power: 0

Nice!! Idle relearn seemed to do the trick. It's nice fixing problems for free, Haha.
Thanks guys! 👍