1990 Celica suddenly very loud engine and low RPM / code 25

1990 celica 4afe 5spd

Hi All, I’m looking for some potential suggestions for debugging a recent development on my celica. Last night I did about an hour of highway driving, and after that I might have done a little harder-than-normal acceleration away from a light (not sure if relevant). About 5 minutes after that I was about 2 minutes away from home when the engine suddenly sounds much different (exhaust / air noise, just much louder), and when I push in the clutch RPM drops to ~200 and stumbles instead of the normal ~550 idle speed. The CEL also flashed on for about a second while moving but then turned off again.

Today I went to check it out, There were no leaks or obviously disconnected vacuum lines or other obvious damages immediately visible. I did the Wire-jump and count flashes of the CEL trick and got a code 25 ‘running lean’. Oil and coolant were of normal levels and color. I lifted it and felt all around the exhaust but could not find an obvious hole, O2 sensor was on tight. I started it and the loud sound is still there, the RPM now at ~1.3k (when usually for a cold start it would jump to ~2k), and it also smells of fuel strongly. Does anyone have any suggestions for tests I can do to try to further isolate the issue?

Thanks for reading! Fingers crossed 🙂