So I have a problem with my car, it's a 2004 RSX (not a Type-S). Basically, a week ago I changed the transmission fluid and took it out on the highway for a test drive, got it up to 170 km/h and when I slowed back down the engine started knocking. When the engine is cold, the knocking noise is louder, and quiets down (but is still there) when the engine warms up.

I took it to the dealer for a diagnosis and 3 days later they called me back saying they have absolutely zero clue about what's wrong. All the fluids are clear (no metal shavings), cylinders run fine and pumps are good. They think it might be something mechanical, but again they don't know.

Their suggestion is basically $2500 for a used engine or $8,000 for a brand new engine.

What I'm wondering is if anyone might know/have some insight as to what this mystery problem could be?

 

what kind of dealership can't figure out a knock lol

Not really possible for us to diagnose your issue over the computer without seeing/hearing your engine and or more description. Does it sounds like a rod knock? A valve tick? or a transmission sound? Can you pinpoint the location of the sound?

 

It's basically a steady thunk thunk thunk sound.

I actually took it to 2 dealers. One was the Acura dealer where I bought the car, 40 min of looking and some valve adjustments they gave up and said to just get a new engine...then charged me $180 for the inspection.

The next dealer was a Honda dealer closer to my house, where a family friend knows the service manager. They checked everything. The pressure for the rod bearings was "very good" so they don't suspect the rods (or oil starvation). It might be a blown valve, but they couldn't locate it if it was (which...maybe is the case since it started right after I stopped accelerating). The noise is, to quote them "definitely from the engine...around the front lower part of the engine".

My Father's friend thinks it might be the oil pump, possibly a damaged spring in a relief valve (even though when checking the pump seems to be in perfect working order).

 

my water pump used to knock and would quiet down after it was warm or driving. dont know if thats relevant to your problem though, just throwing it out there.