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2001 eldorado,2008 DTS,2005 XLR, '96 eldo,'95 eldo,' 89 eldo,'78 eldo,'11CTS-V
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1,716 Posts
Discussion Starter #1
Codes 171 and 174 are lean conditions for one or the other (both) banks.
Codes comes up when entering closed loop; then goes to HISTORY after a short while. Every time (after I reset the codes).
Rear O2 sensor replaced.
Is this a manifold leakage problem that seals itself after warmup?
Or what?
 

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1997 Seville STS, 2000 Seville STS
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1,694 Posts
Looks like it. Its a vacuum leak after the MAF and before the intake valve. Check your bolts for torque, check your vacuum and PCV lines for a loose or cracked fitting, especially any rubber 90 degree fittings in vaccum lines. Your car does not have a plenum between the throttle and the intake manifold, or a divorced MAF like the post 98's do, so it won't be that easy to check those and find it. Its not an O2 sensor code, don't just start replacing them unless you get a DTC directly related to an O2 sensor.
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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68,449 Posts
BUT the throttlebody > intake manifold seal IS a silicone O-ring. :sneaky:

The good ol' choke cleaner spray works to detect leaks in these, too.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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19,270 Posts
does this year have the backfire overpressure valve on the intake?
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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68,449 Posts
Yep - in the passenger end tunnel, a spring-loaded flapper with a seal ring. They get a chip or dirt on occasion and allow a vacuum leak - sometimes noisy. The 2000 and later has a spring-loaded poppet valve in the throttlebody end of the manifold itself.
 

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Registered
2001 eldorado,2008 DTS,2005 XLR, '96 eldo,'95 eldo,' 89 eldo,'78 eldo,'11CTS-V
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1,716 Posts
Discussion Starter #7
Ah, I forgot about the flapper valve. Let me shoot some starter fluid or choke cleaner around there.
Thanks.
Oh, yes I did tighten the plenum. No change.
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,781 Posts
Unless you had a backfire (causing the valve to open) the over pressure relief valve never moves so it is rare that it would get any debris caught in it or have the seal unseated.
 
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