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Discussion Starter #1
I recently built my motor. As such, the chassis and all the electronics have been sitting around for a jolly long time, in the time that I took the motor out, had it built, and turned the car on again. Upon startup, I found that my car is running very lean (wideband reading full lean almost always.) I replaced my wideband o2 sensor, because I thought my wideband was acting up and for peace of mind. Nothing changed. I get a CEL for P0171, system too lean. Upon taking a log with EvoScan, It seems to me like my o2 sensor is not working. I highly doubt this outcome. since I replaced it between my motor being out and it being put back in for peace of mind. Admittedly, it was not a brand new unit. I am just hesitant to blame my o2 sensor. I have attached a log of my idle. I can see that when the car starts, my wideband reads reasonable levels, then slowly gets rich, then swings too full lean for practically the rest of the idle. Does anyone see anything off? Is this just me purchasing a bad o2 sensor? I just want to get a second opinion before jumping the gun and purchasing a brand new o2 sensor.
 

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sounds like a vacuum leak or dirty/bad MAF.
you can test O2 by adding some more fuel (propane, acetylen, brake cleaner... whatever) and see if O2 sensor react and goes on the rich side.

also, you could look at fuel trim off idle (should be less off when cruising if it is a vacuum leak).

good luck!
 

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Discussion Starter #3
I ended up finding the issue. One of the spare bungs in my downpipe was unplugged, resulting in a hole in my exhaust one inch away from my front o2. Plugged it back and now everything is back to normal.
 
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