4Runner Hissing Sound and Fuel Consumption

I have a 4Runner as well, though not a 2000 model. Your symptoms sound a lot like when my intake hose had a leak. Check around the intake manifold and throttle body, especially the hose connections. A leak there will definitely cause higher fuel consumption, trigger the check engine light, and make a hissing noise. Have you tried looking for cracks or loose connections?

Thanks for the tip! I'm not very mechanically inclined. Could you explain where exactly I should be looking for this intake hose, and are there any easy ways to check for a leak? Like, can I spray something on it?

Alright, the intake hose usually runs from the air filter box to the throttle body, which is mounted on the intake manifold. Visually inspect the hose for cracks. As for leak detection, I wouldn't recommend spraying anything unless it's specifically designed for that. Honestly, given the check engine light and hissing, I'd suggest taking it to a trusted mechanic. They can do a proper smoke test to pinpoint the leak and avoid any potential engine misfire.

Thanks again for your help and advice! I took your suggestion and brought it to a mechanic. Turns out it was indeed the intake hose leaking, as you suspected. The repair cost 100€. I really appreciate you pointing me in the right direction!