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Strange O2 readings

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InFlames

20+ Year Contributor
445
0
Mar 7, 2002
Long Island, New_York
Ok, I have a strange problem with my o2 sensor readings. I know the ECU is constantly adjusting the fuel trims so my o2 readings are going from about .20 to .96. The problem is when I let off the gas while driving and let the engine idle, the o2's are around .96 and it stays that way for a while, making my car run bad and sometimes stall. After about 15 to 20 seconds, the o2's begin to go up and down again, but not very well.

The only fuel system mod I have is a 255 walbro that has been working great for about 8 months.

I'm pretty sure it's not an air leak because boost and vacuum pressure are still exactly the same.
 
Originally posted by Coldandafraid
are you venting?

Unfortunately I am (I bought the car with an Apexi BOV). It needed to be adjusted and was leaking when I bought the car. It's fixed now though.
 
Venting is causing it. I tried for a day just to see. It never ran correctly.
 
Originally posted by nowayout
Venting is causing it. I tried for a day just to see. It never ran correctly.

I don't think so, it's been running fine for about two years like that.

I checked for boost leaks today and only found a small one where the upper IC pipe connects to the IC. Nothing big enough to cause my car to stall and run bad.

My fuel trims are High 129%
Med 124%
Low 128%

these are constant and there is no fluctuation from idle to redline!!!
 
Originally posted by forcedfedgsx
im pretty new but 129% thats not cool!!!

Yea, that's what I'm thinkin'. Now I just have to figure out why they're like that. I have a feeling the ISC is blown.
 
its possible your car doesnt like venting anymore, if you got the dump pipe just throw it on and see but thats me always hoping for the simplest answer
 
It's the ISC, I unplugged it and it runs fairly well. I'm just waiting fot the new one in the mail. I bought the car with and apexi BOV and without the return pipe :mad: . If I had the choice, I would definitely NOT be venting (I'm a poor a$$ college student)
 
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