P0172, 900rpm idle after adding over 15gl 2003 Envoy XL

[jsinga]

Possible evap system problem? Only sets P0172 rich bank1 pending code after adding fuel enough to get over 3/4 tank. 900rpm goes along with the code. Don't see high + LTFT. Somehow it sets right after we fill up. Doesn't turn on SES light. Most time code will clear and idle will go back to normal.
We look at data with torque pro enough to see things aren't out wack from normal. What ever causes the code doesn't last long. If car sits next drive cycle the code is gone.
Any idea?

Thanks,
JS

 

[mrrsm]

First Guess...? If your '03 is equipped with the SAIS (Secondary Air Injection System)... look to your SAIS Solenoid on the Passenger side of the Engine Head. If it is getting 'a bit sticky' now... it will allow the SAIS Pump to run longer than it usually would at Start Up. The purpose being is to pump more air into the CAT at Start Up to help make the CAT more efficient.

The one important consideration here is this: Whether from an Intake Manifold Leak ...or from "Excess Air" reaching the O2 Sensors from an over-activated SAIS Pump ... these stimuli will ALWAYS prompt the PCM to Add More Fuel to re-achieve Stoichiometric Perfection... and the obvious response will always cause an elevation in the Engine RPM.

There are some specific posts covering this issue here at GMT Nation that focus on conditions where the P0172 sets... and remains persistent. In those conditions... the diagnostics will focus on the O2 Sensors and when they enter Closed Loop.... vs. the Short Term to Long Fuel Trim changes ...and the weird spikes that can happen within the first 15-30 minutes of driving to trip the P0172 Code. When this occurs ...The SAIS Solenoid might be "The Prime Culprit" to examine.

 

[djthumper]

Three things come to mind on this for me from others that I have seen.


A loose vacuum hose, particularly #8 in the picture.


I fuel filter or the O2 sensor. From what I recall those are the big 3 culprits for this code.

 

[jsinga]

No SAIS (Secondary Air Injection System) on 03.
Checked hoses under the hood. Nothing is loose. I still suspect something in evap system since it only sets pending code after fill up. Also checked for fuel filler neck problem. It was in the gas tank recall and it was replaced.

 

[mrrsm]

Just so you know... Your Vehicle is listed in your Data as being a 2007 version.

About your suspicions concerning the EVAP System involvement... FWIW...This entire linked Thread covers a lot of ground on the topic for the V8 flavors of the Trailblazer-Envoys but nonetheless... you may find something useful there. In Post #6 ... I tried to include investigating BOTH ends of the Evap Solenoid(s) for parts they might be playing in being the cause... even without setting the Codes that would draw your attention to them...in case your have a similar "Front" Evap Solenoid arranged on the 4.2L Engine of your ride:

https://gmtnation.com/forums/threads/bad-gas-cap-or-purge-solenoid.16944/#post-532675

 

[Tdub]

If it happens right after a filling up, my guess is the evap purge solenoid is not closing completely due to being faulty or a small piece of broken up charcoal holding it open. You should not be able to blow through it at all when removed.

 

[mrrsm]

@jsinga ... It will also be worth your while to check out @littleblazer 's suggestions in Post #8 and Post #19 at this link:

https://gmtnation.com/forums/threads/bad-gas-cap-or-purge-solenoid.16944/#post-532675