So I went to clean up the throttle plate & throat on my 05 LS430 that I bought a week ago.

After removing the airbox, I inspected it and saw what looked like a gap between the seam that joins the "lid" to the body of the airbox. I blew through it and sure enough, it was not sealed.

So I went around the rest of the seam and blew air through - the majority of the entire seam, all the way around, leaked air into the airbox.

This would mean that while the engine was running it would get unfiltered air through that seam into the throttle body....

I sealed around the seam with cyanoacrylate and no more leaks, finished the throttle body service and put back together.

Unless they make them like this on purpose, I would suspect that the same heat that makes these things brittle had warped the box and made that seam so it was not airtight any more.

Just an FYI in case you have your airbox off and want to blow through those seams to see if yours leaks. This is the vacuum box and not the air filter box. Over time that small amount of dusty air sneaking in would take its toll on your engine, I would think, because it is 100% unfiltered.

you can just blow on it like a harmonica and tell if its leaking or not, or get technical and plug up all the hoses and pressurize it under water, or whatever you'd like.

I'm interested to hear if anyone else has had a warped air box, i know a lot of these will get the nipples/fittings broken off over time because the heat makes them brittle, i just fix those with brass fittings.