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What’s up guys! First trying this forum stuff so please help me out with this issue. So, when my check engine light came up I got it scanned as soon as possible. I got codes p0171 and p0420. P0420 ( catalityc ) was replaced as soon as possible. I Unplugged the battery for the computer to reset. Light came back up a day later. Scanned again and p0171 was up. I have a cold air intake from bumper to manifold. I’ve been having it installed for more than two years. Has not giving me any issue. Did my research and did as much as I can step by step. I removed MAF, sprayed it down with sensor cleaner, let it dry, reinstalled it and then I unplugged it while the car was on. Car turned off so it’s telling me that sensor is still good. Sprayed water with soap all around the hoses and any gasket to see if my car will idle. Nothing. Bought this liquid from AUTOZONE called CATACLEAN. Used for cleaning fuel Injectors, o2 and catalityc. Used a screwdriver to listen for a clicking sound on fuel injectors. Clicking sound is on point. Don’t know if they are dirty or not. Just cleaned throttle body today. Removed battery plugged back few minutes later light came on. Have not checked o2 sensor yet cause Im hoping it could be anything else but that. But that’s my next target.
Now, today I noticed this hissing sound right on the center of the engine. I tried following the sound to see where it’s coming from started spraying and no rough idle. Car idles rough on it’s own at times when not being worked on. Not all the time tho. So before touching o2 sensor, is there anything that I missed? Please help thank you!!
 

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Man o man, I feel the pain. It's hard chasing an error code that leads to several causes. Going down a rabbit hole with no indication that the rabbit is there.
I found this link which might be a little helpful. It points mostly to the O2 sensors. Most of the useful info is at the bottom of the post.
If you eventually find a fix would you post it to help others?
Error code P0420: What does it mean & What to do? - OBD Station
Good luck.
 

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P0171 possible cause in likely order:

1. Bad, dirty or misinstalled air filter. Inspect, replace or clean as necessary.
2. Bad MAF, even if tested functional. Swap in a known good MAF, reset the battery power, reset all OBDII codes, drive and watch for CE sodes to come back. Replace MAF if bad.
3. Air leaks in the air intake hoses. It would cause hissing sucking sound. Check for tears or leaks on hoses. Spray soapy water on hoses and watch any sucking action.
4.contamination at throttle body, butterfly valve, PCV or EGR valve. Spray clean, test, replace if needed.

Bad O2 sensor would pull a sensor code, not P0171. P0420 can be fixed by adding a plug defouler (extension tube) at O2 S2.
 
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