SOLVED! Random issues: Secondary Air Valve, Stalling, bucking, slight idle issues

NVSparky

Original poster
Member
Jul 19, 2020
5
NV
Hi gang, new(ish) member here wanting to say hello and ask for some help. I appreciate any help you all could offer.

My wife's 2006 Envoy 4.2 started acting up a few weeks ago. It's got several things going on that have shown up together:
P2431(secondary air valve sensor out of range)
Intermittent rough idle when the car is hot.
Intermittent stall at stop light
Intermittent bucking or missing while accelerating

I've done a lot of reading here and TV forum and have tried a LOT of solutions. Here's what I've tried so far:
New Plugs and Coils, AC Delco OEM
Throttle body removal and thorough cleaning
MAP sensor cleaning
PCM reset
Tested injectors resistance with multimeter
Tested fuel pressure
Replaced secondary air valve/sensor/gasket, tested relay and fuses
Tested Secondary Air pump, relay, and fuses

The DTC p2431 comes and goes every 3 or 4 times running the engine. The "freezeframe" for the code shows the engine is off (0rpm) when the code is triggered? Maybe that's normal?

Right now I'm questioning the ignition switch. I've replaced it twice several years ago for different symptoms which were resolved.
And possible bad wiring to the SAI valve. PCM issue?
Deleting it isn't an option with emission inspections here.

Any ideas? 😁

Thank you!
 

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Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
When you did the PCM reset, was it by disconnecting the battery for 30 minutes? Just resetting codes isn't enough, especially after cleaning the throttle body. Maybe also clean you MAF too.

For the p2431, Did you fully inspect the hoses and connections for any leaks? Is the blower working correctly and supplying the proper amount of air?

What kind of testing does NV do? Is it as tough as CA? If it's anything like what we used to have here, which was just roll in, quick check under the hood, plug into the OBD port, check for codes and I/M status and done, you could easily delete this system by having the PCM tuned and the codes deleted for it. From what I see, it's just plug and check. Maybe @djthumper can chime in here on this. I deleted mine early on when we still had testing here and it passed without any issues.
 
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budwich

Member
Jun 16, 2013
2,027
kanata
you could try a "test blockage" mode for a while and see if it changes the rough running / missing. Get a piece of aluminum or equivalent that you can work with tool wise (ie. cut, grind, drill). It doesn't have to be a perfect fit but basically blocks the opening at the valve on the engine area where it is mounted ... basically make it like a "block gasket". This will more or less rule out "massive air leaks" causing issues with o2 sensors which then feed "fake" info back to the pcm which then causes "ugly run data". The light may be on but the engine should run normally IF everything else is OK.

My guess is you have may have a couple of problems... the MAP, either the cleaning or connections (air / vacuum, electrical) have an issue and possibly a leaky / stuck sais valve (more likely non-operational as opposed to leaking / stuck... because it was replaced... it can be bench tested).

For overall run problems, monitor your LTFT / STFT trims at warm idle and medium constant throttle... go from the results.
 

NVSparky

Original poster
Member
Jul 19, 2020
5
NV
Mooseman, I reset the PCM first by battery disconnection. A few days later after some more reading I did it by pulling the PCM fuses for 30 minutes, ignition on with no load(actuators calibrated).
I checked hoses but haven't removed them for thorough inspection. The pump works good. One of the tests I did to test the whole system in one shot: disconnected the suction hose at the air cleaner box. Disconnect the electrical connector at the valve. Turn on the engine, quickly get to the suction hose and feel a little vacuum with your hand. Then plug in the connector at the valve, which opens the valve. Then feel a LOT of vacuum at the suction hose now that it has an open path. I also pulled the pump out and bench tested it. It runs strong. I disconnected the hose at the valve and start the engine and hear the nasty sound coming from the valve until it closes, about 15 seconds later.

Thanks for your reply
 

NVSparky

Original poster
Member
Jul 19, 2020
5
NV
My guess is you have may have a couple of problems... the MAP, either the cleaning or connections (air / vacuum, electrical) have an issue and possibly a leaky / stuck sais valve (more likely non-operational as opposed to leaking / stuck... because it was replaced... it can be bench tested).

About a year ago I have a CEL for MAP sensor. I found a mouse had chewed through the signal wire at the connector. I repaired it with a solder/heat shrink shrink butt splice connector and haven't had an issue or DTC for that since but I'll check it out.

I've checked for vacuum leak with propane. It doesn't hurt to check again.

The SAI valve I'm sure is opening and closing during the cold run cycle. I've verified it by disconnecting the hose and hearing the exhaust feedback for about 15 seconds until it finishes the cycle and closes. This doesn't mean it's not opening later while I'm driving. I like the idea about the block off plate.
 

NVSparky

Original poster
Member
Jul 19, 2020
5
NV
So I'm now getting pending codes p0106 and p0107 (MAP sensor voltage low/unstable). I watched vacuum pressure with the scanner bounce up and down while I was driving.
So I found the wires I repaired last year to the MAP sensor, one of them was broken and making intermittent contact. So I'm hoping this fix will solve the erratic idle, stalling, and loss of vacuum symptoms.
Do you guys know if the PCM references the SAI valve pressure to the barometric pressure from the MAP? I'm curious if the MAP sensor signal being unreliable was related to the P2431 DTC.
@Mooseman @budwich
 
Last edited:

NVSparky

Original poster
Member
Jul 19, 2020
5
NV
So fixing the MAP sensor connector seems to have fixed my P2431 DTC. Apparently the SAI valve pressure sensor is referenced off of the baro signal from the MAP?
@Mooseman
 

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