P0171 and p0174 codes appear around town
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2nd Gear
Joined: Jul 2006
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P0171 and p0174 codes appear around town
Have had the same P0171 and p0174 codes appear on my 01 vette but mine seem to occur when running around town at low idle or after frequent stops and starts. Almost like clockwork. Something about low idle, especially in hotter temps about 90. Can reset them and will stay off. Have clean MAF sensor, replaced gas cap and cannot see any vacuum leaks at least that are obvious? Any suggestions?
Drifting
Joined: Jul 2015
Posts: 1,844
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From: San Jose, CA
Out of curiosity, do you see RPM fluttering up and down at hot idle without you touching the pedal? Especially as you come to a stop, maybe it dips low, bounces up, dips low, bounces up ...
I had an intermittent lean condition on bank 2 that was caused by a failing gas pedal - well, technically, the accelerator pedal position sensor on said gas pedal. It also caused weird bouncing in hot idle RPM, which was a MUCH more direct cause->effect than an occasional lean-on-bank-2 condition.
I had an intermittent lean condition on bank 2 that was caused by a failing gas pedal - well, technically, the accelerator pedal position sensor on said gas pedal. It also caused weird bouncing in hot idle RPM, which was a MUCH more direct cause->effect than an occasional lean-on-bank-2 condition.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,657
Likes: 4,090
From: Cape Coral, Florida
You most likely have a vacuum leak somewhere between you MAF sensor and your TB... have you had the MAF bellows off before it started throwing those DTC's ??...it's NOT a gas cap...that's a completely different system !!...last year I found a vacuum leak at the PCV where the "condensation" metal band (pictured) exits the PCV hose...I removed mine and sealed with RTV....you can take some Brake Kleen and spray it around that area, the MAF bellows (may be torn)
and also around the brake booster too...also look at the purge valve plastic hose at either end (pictured) !!...see if the RPM changes when you spray the Brake Kleen...if you think it's the PCV you can remove and plug that vacuum line, clear the codes and see if they come back...if they don't that's where the leak is !!....ENGINE VACUUM IS HIGHEST AT IDLE...that is when a vacuum leak will be noticed as you have !!
Last edited by C5 Diag; Jun 12, 2019 at 02:42 PM.
Burning Brakes
Joined: Aug 2017
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From: Newark Delaware
Instructor
Joined: Jan 2019
Posts: 215
Likes: 223
From: Atlanta, GA
Had the same issue. Ended up being 4 of the intake manifold bolts being loose. After tightening them to spec, the codes went away. Ended up removing the intake and replacing the 8 gaskets for my own peace of mind, but haven't seen the 0171 or 0174 codes since.
