About 2 weeks after I replaced my regeneration valve that caused starting issues I noticed a noise that sounded like a belt squeal. It would only start when the car got up to temp and would get worse the further I drove. I assumed it had something to do with the work I had done before and that something was rubbing on the belt. It would be very faint while coasting (decelerating), and would disappear with any throttle input. After driving for a while it would make the noise even at idle unless I turned the A/C compressor on. I had no smoke but idle became slightly more erratic and would dip when I came to a stop.
I was convinced something was grinding on the belt but did more research and decided to check my oil cap vacuum and after I started the car it had a strong vacuum but I was able to remove it. Next day I drove home from class and it was loud and wouldn't stop by the time I got home. Tried to remove the cap and it would not come off. CEL came on and I shut it down and ordered an AOS the next morning. I replaced it last night and everything is perfect now. Idle is very steady and no cel. Just a little smoke on initial startup the first 2 times.
I did find it odd that I never really had much smoke on startup or a big cloud when driving while it was failing.
Car was on original AOS since '98 and lasted 118,500 miles. Pretty good from what I've seen.
Replacing it was not fun. A lot of awkward angles involved and not being able to see what I'm doing didn't help. I would recommend cutting the original bellows then removing the hose clamp from the top with the aos out of the way then using a screw on hose clamp to replace it.
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