Help!
I'm loosing my hair over this one.
I have a 2000 Lexus RX300 with over 200,000 miles and for the most part, it runs great.
Recently it was idling very poorly and was getting worse. #4 cyclinder was out and I changed the plugs and I thought that was the end of it, since it took care of the idling and rough running.
As it turns out, the rough idle was masking another problem. When I'm over 3,000 RPM on the road (like getting on the freeway), I get this strange hissing sound and a minor loss of power. The power loss isn't drastic, since I'm still accelerating, but slowly.
I cannot replicate this sound while its standing still.
I've had an exhaust specialist check to see if it might be the muffler or the catalytic converter, but he tells me that those are fine. He tells me that the problem is in the top end.
I've used a thin hose to try to listen for a vacuum leak, while the engine was running, but no luck.
I've cleaned the MAF without luck.
I've changed the air filter as well as the oil.
Grasping at straws, I feel like its a very loud vacuum leak?
The problem with this theory is that I can't discern any leak while parked with the engine running at idle or revved up.
The closet I can drescribe the sound is like, when I took my friend's 1973 Cadillac out (with the hood and air cleaner removed) and stood on it. The secondaries did not fully open and made a similar hissing noise. ... but I'm just guessing.
Any suggestions or solutions for diaganosis or repair would be greatly appreciated!!!!
Many thanks,
Alex
