Celica Hissing Noise

Hissing, you say? Check Engine light too? Hmmm, I had something similar happen with my Celica. Symptoms sound awfully familiar. Any engine misfire along with this? Have you checked your air intake system, especially the hoses around the throttle body? How's your fuel economy been lately?

Misfire, not that I've noticed. Fuel economy's definitely taken a nosedive though! Throttle body hoses, eh? Is there a specific hose I should be looking at? Or am I going to be tracing every single vacuum hose in the engine bay?

I'd wager a bet on the intake hose itself. When mine went, it was a devil to diagnose. The hissing grew progressively louder until it was unbearable. If you’re not comfortable tackling it yourself, I would suggest a qualified mechanic. Ignoring it will only cause further issues. The increased fuel consumption is a sign of that, in addition to the error in the ECU.

Intake hose, got it. Thanks for the tip! Turns out it was exactly that – a split in the intake hose. Cost me 100€ at the shop, but she's purring like a kitten again. No more hissing, and the check engine light is finally gone. Appreciate the help!