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Discussion Starter #1 (Edited)
Thanks in advance for your time and input.

The car:
-1992 n/a 170,200 miles on engine, tranny, chassis

The problem:
-Overall poor acceleration (feels like 50% of normal), with significant hesitation at low RPM.
-Raspy noise corresponding to throttle depression. Present but subtle at idle, or while maintaining speed, but becomes very noticeable when revving or accelerating. The noise is tied directly to revs, and while on the throttle, sounds like holding a plastic grocery bag out the window, with a softer quality. The engine sound itself seems unchanged, and the noise just seems like it's layered on top. No CEL or smoke, normal temps.

Context:
-The car has recently been running the strongest it has in the 5 years I've had it. I drove about 5 miles yesterday, normal route with good roads, no incidents. Started the car today and the symptoms were present.
-The car has always had a bit of raspiness to the exhaust. I mentioned it to a shop a few years ago and asked them to look for an exhaust leak. No leak found, and, with no point of comparison and as it's never impacted anything, I've presumed it was normal. The new sound seems like that regular raspiness, magnified.
-The car burns an amount of oil. Not an alarming amount and I've never run it down to the point where the light comes on. 5w30 synthetic blend. I added a half quart or so within the last 50 miles.

Recent maintenance (all within 200 miles)
-Fuel filter
-Air filter
-Oil change (5w30 synthetic blend)
-New distributor
-Transmission fluid replaced with Lightweight Shockproof

Startup and revving:
This video was trimmed from its original length of 3.5 minutes. It includes driving/acceleration. I'll work on finding a way to upload the rest.

Warm engine, off.
Listen for the buzzing noise. Excuse the frogs.
 

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Discussion Starter #3
A leak definitely seems possible. That was my instinct based on the sound and its behavior. I'd have 2 questions about that. It seemed to happen literally overnight, which was odd.. any logical way to explain that? Other question is how a leak would relate to the acceleration issues I'm having.

Things have been hectic lately, but I'm trying to get another video up that displays the issue better.
 

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.... It seemed to happen literally overnight, which was odd.. any logical way to explain that?

... how a leak would relate to the acceleration issues I'm having....
Hose cracks or gasket disintegrates. Everything has to happen sometime.

Incorrect mixture due to air bypassing the flow meter.
 

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Discussion Starter #5
Thanks for the info. I just looked at my exhaust for the first time, and I see a lot of crappy welds along the midpipe... potentially header too... and I have to imagine that's not a Toyota cat.




Sound seems to be centralized around the weld that looks like its had moisture escaping, surprisingly. Based on that photo, is there also something wonky with the header? That also appears conspicuously non-Toyota.

Music at the end is my phone recording itself playing Spotify, which had Bluetooth'd to my stereo, which was muted, autoplayed, and then disconnected. lol
 

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I guess that you are talking about an exhaust leak. That is not as disruptive as an intake leak, but it can cause the O2 sensor to malfunction, which can also cause bad mixture.
 

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Discussion Starter #7
I wouldn't know how to distinguish between an intake/exhaust leak besides the type and location of the sound. My best guess is it's exhaust-based, around that one trashy weld. Supposing it is exhaust, is your suggestion that the o2 sensor has been/might be ruined? Or that it's temporarily being forced to work improperly?

Based on the state of the midpipe and manifold/header, I'm inclined to replace those regardless, at this point. Can someone point me to a good resource for information/recommendations on this stuff, or exhaust broadly?
 

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...is your suggestion that the o2 sensor has been/might be ruined? Or that it's temporarily being forced to work improperly?

Based on the state of the midpipe and manifold/header, I'm inclined to replace those regardless...
By itself, an exhaust leak does not usually damage the sensor. However, there is no good way to evaluate an O2 sensor except by replacing with new.

Taking care of what you know about is always a good strategy.
 
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