I've got a 2006 Toyota Corolla, 175k miles, automatic, regular oil changes/maintenance. It's been running lean with a P0171 code for a little while, which is my fault. Just recently starting making a low whirring noise when it accelerates from idling, sounds like it's coming from the engine and it's in the same rhythm as the engine. It also just popped a P0420 code.
I'm really hoping the cat isn't bad. Any idea what the issue could be or how to diagnose it? I haven't been able to find reference to the sound online.
If possible please upload a video demonstrating the noise to youtube or a file sharing site and post the link here.
The P0420 is being caused by the P0171, lean bank 1. It's messing up the CAT. Find the cause of the P0171 first, bad MAF sensor, vacuum leak(s), etc. When you fix the P1017 code, put some dedicated CAT cleaner through it to hopefully save that expensive CAT.
Check and see if you have any intake air leaks. Also, check the fuel injectors.
