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Discussion Starter · #1 · (Edited)
Sorry if I’m in the wrong thread, but i just installed the skunk2 catless downpipe and the skunk2 full race catback exhuast and since then whenever i’m coasting with the clutch in or in neutral the idle will surge up to ~2000 rpms, hang, then drop until i’ve come to a full stop and it’ll do it once or twice and level off to usual idle speed 800-1100 rpm depending on temp. I’ve checked the maf and it’s secured, I unplugged the battery, replaced the maf but returned it two days later because it wasn’t the fix.

any ideas?
Edit: I've tried idle relearn, I use 93 octane fuel, I have a cold air intake
Video of the revs:
 

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Try just doing the idle relearn procedure.
1. Disconnect the battery for 15 mins.
2. Start the car and bring it to operating temperature.
3. Hold the RPM at 3k until fans kick on - this is to make sure you are really at operating temperature.
4. Let it sit at idle for 5 mins (I did 10 mins for good measure).
 

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Discussion Starter · #7 ·
Try just doing the idle relearn procedure.
1. Disconnect the battery for 15 mins.
2. Start the car and bring it to operating temperature.
3. Hold the RPM at 3k until fans kick on - this is to make sure you are really at operating temperature.
4. Let it sit at idle for 5 mins (I did 10 mins for good measure).
I've done this a few times no help
 

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Discussion Starter · #14 ·
check the downpipe and exhaust installation check for any leaks
we did when we installed it, and i don’t hear anything under the car like i did when we did have a leak i was thinking we could’ve messed something up leaning over the engine to undo the downpipe but i checked the tightness of everything and make sure there’s nothing disconnected
 

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Discussion Starter · #18 ·
i MAY have fixed it, gotta wait for the P0420 code to come back before i say for sure. can’t really say what it was but after unplugging the battery i took off the cold air intake, put it back on but made sure it was all the way on and tightened it to hell, took off any vacuum lines i saw by the intake or that could’ve been leaned on and jammed them back on, unplugged and replugged everything i saw, reseated the maf and replugged it, and then put the battery term back on, then let it idle for ~20 minutes with no load (Ac, radio, headlights, etc) , she hasn’t done the rev surge since. crossing my fingers this is a permanent fix
 

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Stock 9th Gen Si got it right off the bat.

No i don’t have the money to tune it this yet, but my buddies 2013 si was able to run the same setup in his car with no tune for awhile before he tuned his and said only difference was the sound and less mpg
Guarantee there was more going on than that. Just because you don't throw a check engine light, doesn't mean the car isn't running properly. The idle surging is a symptom of this. Your buddy just happened to get lucky and experienced few negative symptoms. I'm sure the car responded much better once it was tuned.

If you were to look at a datalog of how your car was running compared to someone's with a proper re-map, you'd understand why people say it's mandatory. You are just going to keep experiencing annoying issues until you remedy this properly.
 
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