1997 Prelude, completely stock so far. 220,000+ miles. No CELs. Starting around 6500rpm it will "stumble" but continue climbing. It sounds as if its hitting the rev limiter, but rpm continues to climb. Thus far she's gotten plugs, swapped the ICM from a known good distributor, coil, fuel filter. Nothing has changed this strange behavior. Could it be an aged fuel pump not keeping up at high rpm? I still have great power everywhere else. Could it be a knock sensor? The balance shaft belt is off and its likely the original sensor.

I'm just looking for ideas at this point. I've tried looking via google for a solution but no one else seems to have had such an issue.

 

Sounds like you've started by checking the basics at least. I would replace the plug wires too. I have seen engines run like complete crap from poor quality or simply old plug wires alone. Usually it starts with symptoms you describe. It wouldn't hurt to run some injector cleaner through the system for a few tanks to make sure you don't have build up in the injectors either.

Fuel pumps either work or they don't usually. No CEL would mean it's probably not the knock sensor either.

Does the issue only happen at WOT? Or does it happen at the same rpm regardless?

 

I made a couple observations on the way to and from work today.

- The stumble/flutter is present whether at WOT or at part throttle.

- The stumble/flutter noise is also present after letting off the throttle to shift, so the sound is present under load, and when coasting. This to me rules out any ignition problems and points more towards...IAB's fluttering? I thought maybe the EGR valve was being bounced open perhaps, but with the block-off plate from my old Accord in its place it still made the flutter.

The car regularly gets a dose of Lucas in the gas. It does consume a quart of oil every 1-2 tanks of gas (I'm sure half of it is the oil pan and rear main. Has not been addressed for reasons that while objectively irrational make sense in my head.)

 

The IAB's would be fairly easy to trouble shoot, just pull the vacuum line going to the canister- the fail-safe mode is "open."

 

I've been putting it off, the weather has been miserable and I've been miserable. But on the way home, I stopped and pulled off the vacuum hose going to the intake muffler and capped it. Now, under load it sounds perfectly fine, all the way up to redline. As soon as you let off the throttle though it sounds like a pulse-jet down to...5500rpm or thereabouts. I'm suspecting that check valve that is mounted to the intake pipe is bad? At least now I'm headed in the right direction.