I think the faint brief whooshing sound is normal at cold start. Mine does it, and as you've correctly surmised, that's related to the air pump forcing air through the cat. There's no need to resort to subterfuge to mask that sound when you sell it.

The EPA has rules that the mfgs have to meet, in order to get their emissions type certificate, concerning how quickly the engine meets emission standards immediately after startup. The air pump is part of the mechanism that enables them to meet that standard.

However, it's impractical for the state emissions testing stations to require that you bring your car in with a cold engine for the test (you'd have to trailer it to the station), so they have no way of testing that part of the system, which is why the bypass works. Look for OBDIII diagnostics sometime in the future which will monitor the start-up stuff and throw a code if it is not working. Not there yet, however.

Sorry to revive just an old thread, but do the non VVTI engines also have this problem? I have an 03 V8, wondering if I should be proactive on this.

Thanks
Jose

No, 2005+ only.

Thanks

Has anyone with a 2008 or 2009 had this issue?

Yes on the 2008-2009 AIP SAIS pump issues. This problem affected all 4.7s from 2005-2009 on the 4Runners.

I pull my ground cable off battery to reset and get out of limp mode. I can drive quite a while before it happens again. Does this mean the valves are closed during this time?
I would like to install the Slyfox Bypass which I THINK can only be done with valves closed.

Best to email me your codes…..but in general….if you have limp you will need blockoff plates.(and bypass)

This is why it's a great idea to do the AIP bypass proactivly. I installed it from @slyfox75 shortly after I got the truck (2007 v8 bought used in 2014)