Hello everyone. I've been searching for hours and can't really find the exact issue I'm experiencing. Let me first say that I have a MY00 with 82xxx miles which I bought about 4 months ago. It came with a crappy eBay exhaust and a CAI, and I installed a test pipe two months ago. As of about 3 or 4 days ago I've been experiencing a lack of power throughout the powerband, most noticeably below 5k. I don't think it's clutch slip because it seems to rev at the same speed it used to, maybe even slower. Here in FL it's been pouring rain every single day and I haven't been able to avoid it. But I am also very careful about getting on the gas and large puddles in the rain with this intake because hydrolock scares me lol
Anyways, I've also been noticing this rattling noise from the exhaust which started maybe 2-3 weeks ago. It's a very loud hissy-rattle that comes on around 3.5-4.5k and goes away after (or at least my exhaust drones it out), which has had me wondering if my mufflers are shot/clogged.
But here's the real issue. Two days ago it had stopped raining and I was really irked by the fact my car felt so slow. I attempted to take it into vtec to see if everything was okay up there, but at about 5.5k my car stumbled. Like almost popping from the exhaust or something and it wouldn't go any faster. I threw it in neutral, and at the suggestion of my father, went to the store to grab some stuff to put in my gas to take out the water. (His theory was bad gas or a possible leak from the gas cap). Then yesterday I take it out for a drive, and it's super hot and dry outside... VTEC engages fine, BUT the car still feels sluggish, so I'm thinking maybe it was the gas?
However, Last night I was coming home and as it was just starting to rain, my car stumbled again right around 5.5k. WTF.
Now I'm about to check a few things, especially spark plugs, compression, etc., but I also just read a post where someone had a muffler that was bad and it was holding water or something. Which would make sense, due to the crappy weather, crappy exhaust, and that strange rattling.
My other fear though is that the intake sucked up some water and I'm losing compression? The things is that I've driven in the rain many times before and never encountered this issue. Idk. Any help or guidance would be greatly appreciated.
Thanks for reading the novel lol

 

MAP Whack? Does the car idle ok?

 

I forgot to mention that I have already done the MAP whack and changed my oil. It idles fine, no real difference there.

 

I experienced exactly this in my old AP1. I have experienced similar symptoms in other cars as well with the solutions all being different but this is what helped my s2000.

Had an 02 ap1 with 100k on there that showed the exact symptoms you are talking about. One day noticed low power down low (not due to lack of torque or heat soak though), and a heavy skip/stumble around 5.5/6k. Happened at moderate throttle input. It happened for about a week straight, and being concerned with the noticeable power loss, I decided to have a look and see if there were any visible issues. Checked timing, installed plugs, did valve adjustment, etc etc. All the basic troubleshooting was complete. Never found anything, then thanks to s2ki I eventually found out it was my connection with a sensor.

https://robrobinette.com/S2000ValveAdjust.htm

In the diagram linked above my issue was with the sensor labeled TDC2 behind the valve cover towards the firewall. Found a weak connection and as soon as I had that squared away, felt like I bolted on a lot of power haha.

Not saying that your issue is the same as mine, but we did have similar symptoms. It's worth a shot and a look. Good luck, keep us posted if you end up fixing it so when people search and see your thread they can have a solution too

 

Thanks for the response, I will definitely check on that sensor! That would be fantastic if it was that simple.
Just thought I'd give an update. I checked the plugs this morning and all seemed well. Couldn't do the compression test bc I didn't have the tool, so I put everything back together to drive to the store....
And sure enough, it feels great, maybe a TAD slower but hardly even noticeably. VTEC engages fine, but best of all there's no loss of power down low. It feels like it wants to rev up finally.
Only difference from last night is that today is dry and HOT.
I'm really starting to suspect it's that CAI filter drying up. Maybe going into VTEC there wasn't enough air being sucked in for it to engage?? Still confused on that bit.
Anyways I'll keep everyone posted!