Idle air control gasket

tyler

Original poster
Member
Aug 25, 2017
58
Boston
Hey guys, I pin pointed an issue that leads to the idle air control valve. Before I purchase a new one, I want to take the one already there off and clean it out. I can't seem to find an idle air control gasket that will fit the TB. There is obviously a gasket for the IAC right? I don't want to take it off and need a gasket. If anyone knows if I can purchase a gasket online please link me.

Thanks!
 

Sparky

Member
Dec 4, 2011
12,927
The inline 6 on the Trailblazer does not have an idle air control valve. Those only existed on cable-driven throttle bodies, but these are PCM controlled "drive by wire" electronic throttle bodies. To adjust idle air the PCM just adjusts the throttle blade directly.

What issue are you having, exactly? It may simply be that you need to take your throttle body off the truck and clean it really good. Disconnect the battery while doing it so that the PCM will reset.
 

tyler

Original poster
Member
Aug 25, 2017
58
Boston
That's good to know, thanks!
As for issues...
  • Everytime I put gas in my tank, I try to start it once and it won't, second try always works.
  • More noticeable when cold out I feel, when I start the engine on a cold start, vechile shakes a little like it is going to stall, rpms go up and down. Almost sounds like the engine is out of breathe about to die out (or getting to much air.) When I start vechile while engine is warm this issue is extremely mild, if not even noticeable at all.
  • Sometimes when vechile reaches operating temperature, and the car is idling, as if it was in park and reached operating temperature, the vechile will stall out.
  • Uses more fuel than it should I believe.
  • Evap small leak and large leak code detected, also p0171 system too lean bank 1.

I'm pretty sure this is due to a bad IAC, perhaps maybe stuck open? I already cleaned throttle body, checked for hose leaks, changed purge valve and other evap valve, etc.
 

Sparky

Member
Dec 4, 2011
12,927
Well, there is no IAC, so it can't be that.

System too lean means you've got an air leak someplace and that can lead to your idle and running issues if the leak is bad enough. Could be also a bad O2 sensor just throwing false readings. But I'd look for leaks first before messing with the O2 sensor. I'd be checking for gasket leaks around the intake, or for cracked vacuum lines, etc. Use little bursts of spray of some sort around places and see if it affects how it idles. A surge in idle after spraying a small amount of carb cleaner someplace would indicate it is leaking in that area. My guess is it improves when it warms up because whatever leak is there closes off partly when it gets warm. How did you check for hose leaks? Do you hear any hissing when the engine is running?

It could use more fuel than it should if it is trying to correct for a lean condition. Make fixing that your priority. That could correct all the other running issues you're having.

Evap small and large leaks won't affect how it runs, but they're annoying. Small can be caused by a fuel cap, or something really irritatingly tiny like my coworker has run into. Large leaks though can be easier to locate. I'd check your fuel fill neck and hose for starters there, mine rusted and caused issues with leaks (and started dumping fuel on the ground, that was fun).
 

tyler

Original poster
Member
Aug 25, 2017
58
Boston
My apologies, I meant air pump check valve. Does that sound right? Could these symptoms be due to the air check valve?C7F6CBE2-AA7B-4FD9-8B39-4532B710EE48.jpeg
 

Sparky

Member
Dec 4, 2011
12,927
That's for the SAIS (secondary air injection system). All it is for is to heat up the cat faster on cold startup for emissions reasons. Not every GMT360 even has one (my 02 did not). Does yours? If so, check the hose that goes between it and the air box The gasket goes on the exhaust side, but it could possibly throw off O2 sensor readings depending on how it leaks (sometimes an exhaust leak can let air get sucked into the exhaust stream instead of pushing exhaust out a leak).
 

tyler

Original poster
Member
Aug 25, 2017
58
Boston
Yes, mines an 06 and I have one. I should take a couple pictures of my engine and show you.

Is there a way to test the air pump check valve?
 

xavierny25

Member
Mar 16, 2014
6,324
Staten Island, N.Y
The pump is under the driver side of the truck.20180302_142941.jpg
This is a pic of the whole system I removed from my 08 Envoy. Had it tuned for its codes.
 
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tyler

Original poster
Member
Aug 25, 2017
58
Boston
Good to know will use this pic and info when it gets warmer out so I can do it. Thanks.
 

BRomanJr

Member
Dec 9, 2011
371
The SAIS (secondary air injection system) certainly is one suspect, mainly if the Check Valve not closing properly..
Because you have issues right after filling the tank and large leak detected code, I suspect the Purge Solenoid on the side of the engine may be stuck partially or fully open. This can allow vapors from the Charcoal Canister to influence the Idle mixture right after you fill the tank and make it leaner at cruising speeds. This can be complicated IF you also have a bad Vent Solenoid near the gas tank.
Another item to check is your Fuel Pressure Regulator on the fuel rail.
And I agree, as mentioned above, the Front O2 Sensor could be defective or "lazy" and lying to the ECM.

The processes for checking each of these has been covered and should be available using a search. Hope you find the issue(s) soon before frustration sets in.
 

Sparky

Member
Dec 4, 2011
12,927
Well, he did replace the purge valve already, which I assume includes the solenoid.
 

BRomanJr

Member
Dec 9, 2011
371
Well, he did replace the purge valve already, which I assume includes the solenoid.

Yes, thanks, I see that now, my speed reading is getting worse.
He also mentioned "other evap valve" probably the vent valve.
 

tyler

Original poster
Member
Aug 25, 2017
58
Boston
Hey guys just wanted to let you know I replaced the purge valve again ( I already replaced purge 4 months ago) and after 25 miles my engine light turned off, and all my symptoms went away on my TB. What could've been faulty on my purge? What made it go?
 

Sparky

Member
Dec 4, 2011
12,927
Defective part would be my guess. What brand did you use the first time?
 

Mooseman

Moderator
Dec 4, 2011
25,344
Ottawa, ON
Another reason we just delete that whole system. Just problematic and mostly useless.
 

tyler

Original poster
Member
Aug 25, 2017
58
Boston
Can I delete mine? Is there a guide on this site somewhere that could show me? That would be cool.
 

Mooseman

Moderator
Dec 4, 2011
25,344
Ottawa, ON
No guide but it's fairly easy. There's also this thread that explains and shows it a bit.
Removing Secondary Air Injection System
Just remove all the SAIS hardware, put a blockoff plate from a 2002-2003 or make your own and have the codes tuned out. Lime-swap.com is the cheapest at $99. Can also do other stuff to the tune at the same time like remove torque management and firm up the shifts. Also recommend having the fan codes deleted so you can use a thermal fan clutch instead of the trouble prone electro-viscous clutch when it fails.
 
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Sparky

Member
Dec 4, 2011
12,927
He replaced his purge valve again, not the SAIS stuff.
 

Mooseman

Moderator
Dec 4, 2011
25,344
Ottawa, ON
Umm OK. This thread was about the SAIS so...
 

tyler

Original poster
Member
Aug 25, 2017
58
Boston
I know sorry guys lol. Is it worth getting the haynes trailblazer book for an entry level guy like me?
 

Mooseman

Moderator
Dec 4, 2011
25,344
Ottawa, ON
Why? Get manuals free in my signature.
 
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Mooseman

Moderator
Dec 4, 2011
25,344
Ottawa, ON
04+ had SAIS so it should be in the manuals. If not, not a big deal as there isn't much to the SAIS and most of everything else remained the same.
 

sunliner

Member
Mar 25, 2012
365
not sure if I understand the system correctly..but if there was a leak in the SAIS hose, would it matter, so long as the valve is working and closing when indicated?
 

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