2002 C2 throwing check engine light codes P0491 and P0492. Secondary air injection system insufficient flow. It throws these codes when I am at a stoplight, engine idling. The RPM's will drop for just a split second and the CEL comes on. The light comes on pretty much right away after the drive cycle completes (and I am idling). The car started having this problem after I changed the air-oil separator, though I am not sure if that is related. Though this problem predates this repair, I just changed one of the cats too. The car runs great with the exception of the occasional stumble at idle.

Is this the obvious vacuum leak (where?), or does it sound like something else?

Thank you for the help!

 

Can you hear the SAI pump running at cold start? If yes, it's likely you have a problem with the SAI valve, changeover valve or vacuum source.

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I'm not sure about the SAI pump... what does it sound like? Where is it located?

 

It sounds like a small handheld vacuum at the rear left of the engine bay. You should hear it running at cold start for a minute or two. Just search SAI pump on this site and there will be many threads.

 

Ok. I cold-started the car this morning. The SAI pump came on and ran for a couple of minutes. Then it shut off. Seems like normal operation from what I have read. What next?

 

Next steps are more involved. You may want to check out this link, do some scanner troubleshooting before tackling the vacuum system.


https://rennlist.com/forums/996-foru...t-ready-2.html

 

I had another engine stumble this morning... pretty pronounced too. The car was was at idle and fully up to temperature. I heard the SAI pump come on and immediately felt the RPM's stumble after that (it recovers quickly). The light didn't come on only because I had just reset it and it has not yet completed its drive cycle. Perhaps there is a hose disconnected or improperly installed (after changing the AOS).

 

You are going to have to check all of the vacuum lines associated with the secondary air injection system. I remembered after I replaced my AOS, I forgot to reconnect one of the vacuum lines to the intake plenum, It's a tangled mess of hoses, check valves and connectors.

 

goodluck, just got this taken care of at my local indy literally this past wk. $950 out the door to basically replace everything but the SAI pump itself, which is running fine.

 

Good to know. I suspect I'll spend a bunch of time tinkering around in there hoping to stumble on the failed line or component. But I may end up at the shop too...

Great picture to get me started though!

 

Need some help. My vacuum canister has 2 spot for a vacuum line to connect.....can someone tell me what is suppose to connect to what? Also,

What is suppose to connext to this? My assumption is that it would fees the vacuum caniater. Thanks

 

Where your arrow points to shoild connect to the SAI changeover valve, which in turn connects to the vacuum canister. That changeover valve is deep there right next to the vacuum canister.

 

https://rennlist.com/forums/996-foru...omponents.html

 

thanks, I will check it out tomorrow....no doubt this is causing my codes

 

That fixed it! (Fixitguy996) connected the canister to the changeover valve as recommended with a new section of hose. And that seems to have banished the check engine codes! Thank you to everyone here who helped us out!