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Solution to Too Lean P0171 & P0174 (Mazda MPV 2002)
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IamAdam
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PostPosted: Thu Jun 11, 2015 8:51 am    Post subject: Solution to Too Lean P0171 & P0174 (Mazda MPV 2002) Reply with quote

Here's a solution to the P0171 and P0174 problems (too Lean (Bank 1 & Bank 2) that I have been meaning to post for some time. About a month or so ago, I had been having a CEL issue and had been trying to get it solved so that my 2002 Mazda MPV could pass inspection. I read online about a lot of things, like replace the oxygen sensors, and nothing seemed to work. It seemed likely that it was the PCV valve elbow everyone talks about, but after further inspection and pulling things apart, that wasn't the case (although the hose down there was a bit loose; thanks zip ties!).

Anyways, I started looking around at the air coming into the engine to check for leaks. I did find a small vacuum hose that was cracked and leaking which comes from the back side (towards the cabin) of the engine (not the one from the top) so I went to Autozone where you can purchase vacuum hose by the foot (they'll cut it for you). Couple bucks. But that didn't fix the problem ultimately after I replaced the old hose with the new one. If I recall correctly, that did get rid of one of the codes (can't remember which).

So then I started looking at where the main air goes after the air filter into the engine to trace the air. I noticed a tee that branches off of the top of the main flow (not sure what it's called) and one hose goes to the back side of the engine and one to the front (see dotted lines in picture).



Each hose ends up being connected to the engine by an elbow. Upon further inspection, this is where the problem was for me. The elbows were corroded. When I removed one of the hoses, the elbow easily fell apart. They were both in pretty bad condition.





The front one is easy to get to by the spark plugs, but the back one took some contorting on my arm and the temporary removal of some obstructions.

I went to O'Reilly Autoparts and purchased two elbows I found there that appeared to be the same size as the elbows I was replacing.





I replaced both elbows and put them back as I found them. They both fit snuggly and after resetting the engine codes, I drove the van around until the van computer until the powertrain drive (or whatever it's called) fully reset and said that I didn't have any codes anymore. I took it to jiffy lube and it passed this time! Never had a problem since. I hope this post helps somebody cause it took me a while to figure this stuff out. This forum has been really helpful so I thought I should definitely give back. Good luck. Let me know if you have any questions. Hopefully I can help (I ain't a mechanic).

"Contradictions do not exist. Whenever you think that you are facing a contradiction, check your premises. You will find that one of them is wrong."
-Ayn Rand
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Rallywagon
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PostPosted: Wed Jan 04, 2017 11:26 am    Post subject: Re: Solution to Too Lean P0171 & P0174 (Mazda MPV 2002) Reply with quote

Thanks for this posting....this may be my problem. Because of the path of the air, spraying starter fluid (ether) may not cause the change in idle that most vacuum leaks would see. The ether gets drawn through the engine...diluted.

Thanks again.

2002 ES Four Seasons
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drm7
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PostPosted: Thu Dec 06, 2018 7:35 am    Post subject: Re: Solution to Too Lean P0171 & P0174 (Mazda MPV 2002) Reply with quote

I'm getting the exact same codes now and I've replaced other rotting rubber components so maybe this is it for me. Thanks!
2003 Mazda MPV LX - sage green, 4 seasons pkg, rear step, rear a/c, side airbags, roof rack, fog lights, traction control
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