Random engine knocking

[payam972]

Random engine knocking, edit now with video

Today I was driving and I heard a knocking from the engine. Pulled over, the car lost idle and died. started it back up and the sound was definitely coming from back there. When I revved it, it got louder. Then a few moments later it went away and didn't come back again the rest of the day. First time it's happened, no loss of power, car drives perfect.

Now I don't know if I'm imagining but seems to be a very very light rattle sound under the engine cover-where it says vtec. Car still performs perfect.

Any ideas what It could have been?
<iframe width="560" height="315" src="http://www.youtube.com/embed/yipdEhLuJ5I" frameborder="0" allowfullscreen></iframe>

 

[payam972]

sounds like something is loose in there

 

[ScienceofSpeed]

It is very hard to hear from your video. However, if the sound is erratic (comes and goes, not tied to engine speed) a common source of top end noise is the lost motion assemblies sticking. These are devices in the cylinder head that keep pre-load on the VTEC rocker when it's not engaged. When they stick, the VTEC rocker flops around, and bangs on the LMA until it loosen and unsticks. We make a part that addresses this, and won't allow it to happen again:
http://scienceofspeed.com/products/engine_performance_products/NSX/ScienceofSpeed/LMA/

I didn't hear any bottom end knocking, but the valve chatter is very loud. This can simply be the rocker - valve clearance requiring adjustment (which should be done ~ 15k miles) or may just be the sound the camera is amplifying.

-- Chris