This morning while driving, I got up to around 3k rpm, and suddenly the car shuddered, and starting doing the typical VTEC failure mode of not letting you rev past a certain point, creating a pseudo redline. Except the moment it happened, my tach suddenly stopped working entirely, and the car was just running like ****. The best way I can describe it is if all of the engine sensors simultaneously stopped communicating, as the coolant temp also dropped to 0. It was almost impossible to drive, complete loss of power at anything over 1/4 throttle, and sometimes by completely lifting off the throttle it would actually go faster. There's only one CEL code: knock sensor low voltage.

Some troubleshooting steps I've taken: Cleaned battery terminals, checked voltage on battery when running and revving (14.4V), had battery tested, replaced a frayed ground strap, checked that the block is grounded to the negative terminal on the battery, left battery disconnected for some time.

Here's the rundown now: When I start the car, it seems fine. No rough idle, no weirdness, except that the battery light is on, and the idle acts really strange (floating around, sometimes will rev up to 3k rpm on it's own). Driving it feels normal except that when the clutch is pressed, the car revs up even without throttle. It comes right back down, but still is a weird behavior. Then, after a while, if I hit vtec, everything goes to ****. The temp gauge and tach both fail completely, the battery light turns off and everything goes haywire, with the car running like **** and impossible to drive.

I imagine this is an electrical issue, hopefully not the ECU itself? Could it be that the VTEC solenoid's wiring is messed up and that's messing with a ground for the ECU's sensors?