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Discussion Starter #21 (Edited)
Well lads, here's an update. My LTFT is back to sky high 34% at idle BUT the STFT are in the normal range when driving at highway speeds. Can I safely assume that I have a vacuum leak based on these symptoms and everything I have done and replaced?

I have ordered replacement vacuum lines and clamps, OEM Toyota parts.

I have not checked for an exhaust leak, yet. I will pull the mid pipe and replace the gasket after I do the vacuum lines.

I also have not checked my fuel pressure. So far we have been through 2 OEM MAFs, one a known good unit from another car that runs well, and one aftermarket MAF. The MAF -!: FT numbers never change between them.

My STFT is high at idle and falls with RPMs
 

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Discussion Starter #23
Introducing propane to the intake duct causes STFT to drop down and for bank 1 sensor 1 O2 sensor to spike in voltage, showing it is richening up.
 

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Discussion Starter #25 (Edited)
I have not had any success with the propane in making the fuel trim change when pointing it at the intake components to identify a leak. Only when I introduce propane to the intake tube does the fuel trim change. However, I did just bathed the throttle body assembly in carb cleaner and I got a little blip of a reduction in short term fuel trim *but* the intake pipe joint is directly under that point and it is possible it got sucked into the intake pipe before the MAF and I might have tricked myself into thinking there is a vacuum leak there. I will continue to investigate.
 

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Discussion Starter #27
I took apart the throttle body assembly and cleaned it out with. There was lots of crud in the IAC. This resulted in no change to my LTFT.

I then took the mid pipe off and re-aligned it with the header. My LTFT is now down in the 15.6-18.8 range at idle instead of the astronomical 34 I was getting earlier today.

I'm getting really frustrated with this car.
 

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Discussion Starter #29
The car squeaked by in passing an emissions test but my LTFT is still 18+ so I will investigate further. For now, the CEL is off and I have no codes and the onboard emissions monitors all passed.
 

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Discussion Starter #30
The exhaust header to mid pipe collection flange is leaking as evidenced by soapy water sudsing up with a shop vac introducing positive pressure from the tailpipe. I don't know if the exhaust manifold gasket is leaking itself but I'm going to take it off anyway. I don't want to miss anything.
 

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Ah ha! Good find and good way of finding it. That's not a hard gasket to replace usually and it's fairly inexpensive. Fix that and it's possible the fuel trims will become normal again. It would make sense that at idle air would more easily get sucked into the exhaust through that since there's little flow, that air would add oxygen which would tip the sensor to a false lean reading. While driving there's enough exhaust flow to make that slight introduction of air much less proportionally or even reverse it into an exhaust leak.

The Felpro exhaust gasket I used on my Celica for a similar connection worked very well and looked just like the dealer part. It kind of looks like a donut made of brillo pad in a cone shape with some kind of wax binder, avoid the ones that are made of a hunk of graphite.
 

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Discussion Starter #32
I pulled the pipe off and couldn't seem to get the exhaust flange gasket off so I'm taking it to a trusted shop with an explanation of what I've been going through.
 

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Discussion Starter #34
Ok I got the gasket off, i had to mutilate it to remove it.

I am going to put on a Fel-Pro 61124 flange gasket to try to get this thing fixed.
 

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Discussion Starter #35
I installed the new gasket and ran a soapy water test. The flange still leaks. Is it necessary to replace the flange mounting hardware as well?
 

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Typically no, as long as the springs are in good shape and not flattened. I think they're available as a bolt kit or by themselves, I guess it wouldn't hurt to replace the springs but you shouldn't need to. The bolts are called shoulder bolts because of that thicker non threaded section, you tighten them down till the shoulder bottoms against the flange and the spring is what holds tension on the seal. Try driving around some, maybe the gasket seals better once it heats up or something. Any change in fuel trims?
 

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https://www.motor.com/magazine-summary/internal-engine-condition-vs-fuel-trim/

Something to look at, could you have a leaky intake valve? Skim to about 2/3 down to see how that could cause a lean trim.

Does that engine have an EGR valve? If that's leaking exhaust into the intake it would cause an internal vacuum leak and push things lean but you wouldn't necessarily get it to show up by adding fuel around the outside of the engine.
 
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