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I would try replacing the oxygen sensors. You have gone nuts to the wall on this thing checking for leaks, etc. Go with Denso, not aftermarket.

Also, despite its seemingly working, watch that aftermarket Walker MAF sensor. I know you tried with another OEM one from another car, but I do not trust Aftermarket MAFs, they fail prematurely, as do aftermarket o2 sensors.

Replace both O2 sensors with Denso. Keep the Walker MAF. Or if feeling rich, replace both o2 sensors, and the MAF with an OEM as well (more preventative.)

What else could it be? You have done like everything else.
 

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Discussion Starter #62
O2 sensors were replaced with Denso at the beginning of this trouble. Not using Walker MAF. Using OEM MAF. 2nd OEM MAF showed no change in high long term fuel trim.
 

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O2 sensors were replaced with Denso at the beginning of this trouble. Not using Walker MAF. Using OEM MAF. 2nd OEM MAF showed no change in high long term fuel trim.

Opps, my bad. But are we sure he replaced the downstream sensor? I saw it mentioned earlier but he said if the code persisted, he would replace the o2 sensor and/or the cat. So if he only replaced the cat, and did NOT replace the downstream sensor?


If he did, then he doesn't need a mechanic to fix this, but a priest since this thing is possessed and needs a exorcism.


Update: I'm lost. You have. damn.....I have no idea.
 

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Just out of curiosity, and this is probably a really stupid question, but is this a California emissions echo. Is it 49/50 State Federal. w/ respect to what catalytic converter you had just installed and the car's ECU. I was just wondering if by some weird chance it was a California car (California ecu) with non california cat that might be causing this. I don't know if they made echos 50 state or 49 state w/ California builds, or whatnot. No idea if ECUs are all the same if 50 state/federal/Canada,etc.

I'll go away now.


edit: nm, I think they are all 50 state/epa/california.
 

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I've been thinking about this and it's driving me crazy. You have redone the exhaust again. You could try running some seafoam, and let it smoke to see if any is coming out of exhaust still, if there is still a leak. I'm sure you have inspected the plastic intake manifold for leaks. You pretty much done intake/exhaust throttle body mating surfaces/gaskets, so maybe less common areas causing the possible leak (intake manifold assembly?), intake hose, micro-cracks, etc., air filter box/assembly, etc. Would a gas cap cause this?
 

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Discussion Starter #66
Update: I was watching my scanner data stream for LTFT and STFT while pumping my brakes with the car stopped and in gear but parking brake set. My STFT shoots up to 19.5 with the brake pumping action. Whomever it was earlier in the thread that mentioned it could be an internal vacuum leak in the master cylinder, you might be right. I will investigate further.
 

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My mothers 2000 corolla with the metal intake has the same issue. Im wanting to fix this for her!
 

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Discussion Starter #68
Update: intake manifold replaced. No change. Now I'm dealing with a persistent, mystery P0303.

I have swapped the coil, plug, and injector to another cylinder and the misfire is not following the code to the other cylinders. I'm about to set this car on fire and push it over a cliff.

Compression is good and uniform.... about 140psi across all cylinders.
 

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Update: I was watching my scanner data stream for LTFT and STFT while pumping my brakes with the car stopped and in gear but parking brake set. My STFT shoots up to 19.5 with the brake pumping action. Whomever it was earlier in the thread that mentioned it could be an internal vacuum leak in the master cylinder, you might be right. I will investigate further.
How did this turn out? I'm having the same issue with my Corolla. I travel in the morning in relatively light traffic and don't use the brakes much and my fuel trims are low. I'm the afternoon I'm in constant traffic and this is when my stft was at it's highest. I started using my handbrake after I was stopped while in gear, foot off the pedal and stft would drop to normal readings. If I sit at the light with the brake pedal pushed it will climb as high as +15. I went through everything on this car just like you did except the catalytic converter which needs to be replaced but I wanted to find out what caused it to go bad first. Hopefully the booster is the issue.
 

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Try this, while the engine is idling. Monitor the STFT and LTFT.. Then poke the wires of the ECM with your finger. If the trims change.. The ECM has poor connection to the harness.
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