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It feels like I have tried everything to fix this problem I have a 2000 civic si with a b18a1 swap. The problem, when the car is cold it will have a rough start (stutters) then kicks up to normal idle until it starts warming up then the idle will bounce between 150ish rpms to 1000 rpms constantly when the car idles down to 200 rpm the engine shakes the lights dim and it feels like it is about to stall although it never does. while driving there is no power loss just when i go back to an idle which is when it goes right back to surging. I have so far changed the plugs, changed the idle control valve, adjusted the idle speed screw, checked for vacuum leaks and changed one line that looked like it had an issue still no help I cleaned the entire engine (throttle body, crank case, and fuel) with seafoam which seemed to help for like 20 mins or so then boom right back to the same problem I was told my alternator could be going out so i got it checked it came back as a good alternator on the test although the guy says sometimes it wont read as going out until its gone all the way. I have reset the computer to see if that helps it did nothing. I heard it might be a fuel pressure problem but i figured it would effect the car all the way through the powerband and my issue is only present at idle also usually when there are problems with fuel there will be other signs of it which i am not seeing. even touching the gas in the slightest will fix the problem. Oh, and by the way theres no check engine light on which makes everything oh so much harder if any one has any suggestions please let me know this is getting really old lol.