Hey guys, I purchased a 99 Acura CL back in June, and about a month ago noticed a "rattle" developing under the hood. I figured it was my cat / heat shield / something stupid rattling, but upon further investigation I think it's a bit more serious than that.

Cliffs:

-Only happens between 1500 - 2000 RPMS
-Happens in any gear, but certain gears I'm at 1500-2000 rpms longer than others (i.e, first gear you pass 2,000 rpms pretty quick. But when I'm in 3rd gear driving down the 30pmh road next to my house, sometimes I happen to be right in that band for a decent amount of time. So the rattling continues
-Generally only happens when I'm on the throttle. When I'm not accelerating, I idle around 1,000 rpms so it doesn't do anything. And if I'm above 2,000 rpms and then drop, it will rattle real quickly but not long at all.
-It shouldn't be drivetrain related, as it doesn't happen because I turn the wheel / shift / anything else..

I've been trying to figure out what it could be. What parts of my engine only move when I accelerate / decelerate? Intake / throttle body, maybe.. Valves? Could I need a valve adjustment?

Thoughts, theories, input, advice, warnings, and anything else will be much appreciated and +rep will be handed out I do all my own work on my Integra, rebuilding transmissions / replacing the head gasket and more, so just about anything I can do myself, so feel free to throw out some suggestions.

 

check your vtec fluid. sounds low.

 

^ asshat

OP;
Does it happen if you rev the engine at those RPM's while the car is not moving?

 

is there a snake in your boot?

 

If it rattles when you rev the engine with no load (in neutral) then get under the hood and operate the throttle cam with your hand so you can get a better picture of where it's coming from.

 

Based on when it happens (at certain RPMs), its probably one of the components that is run by a belt... rollers/pulleys/tensioners/water pump on your timing belt, AC compressor/generator/ps pump/misc rollers and tensioners. Get a stethoscope or, if you dont have one, a poor man's stethoscope (something long and metallic like a screwdriver) and try to pinpoint the noise.

Also, if it hasn't been done yet, your timing belt is overdue (85k-105k miles or 7-10 years), so it's likely something on that system if it hasnt been done...

Also, check all of the motor mounts and heat shields. Could need a valve adjustment, but not likely...

let us know what you find so we can help