115K 4x2 v8

When you start it motor makes a loud whirring noise for 20 seconds or so than it stops. Sounds like a electrical motor or a fan of some kind. Best guess it sounds to be coming from middle of motor like in the intake manifold. Truck runs and drives fine no CEL.

Search did not help because I don't know if i spelled "whirring" right.

Thanks

Follow up:

I typed this after changing oil and it was the 1st and 2nd start up while cold. I had truck idling while I posted this, went back outside turned it off and on and no noise. Just posting whit I see.

This may sound stupid but, do you have XREAS on your Rig?

Thats the corner to corner shock thing right? I dont believe the 4x2 came with that. Why?

What year is your 4Runner? Sounds like it's the air pump system going bad. I had the same thing but installed a bypass module to fix the issue.

Ah okay, because if you did, that would be something to look at(Process of elimination). I say this because sometimes I can hear this whirring noise, which happen to be the XREAS doing it's thing.

PS: Sorry, I didn't catch the 4x2 thing from the get go..

Yeah, the emissions pump system.

2006
I like bypasses.

Where is this pump? Can I default it on to see if its the sound and how?

This is the engine fan.

During start up you get a big whirl sound because the fan comes on and then after a few seconds stops.

My Tacoma did this too.

Completely normal.

This is really loud. Had truck for 6 months I think I would have heard it before.

It's located UNDER the intake manifold, so a proper fix is expensive. There are a couple bypasses: cheap one involving a relay, resistor and some wiring, or a $200 solid state module that tricks the air injection system into thinking conditions are such that it should NOT run (keeps it in stand-by mode), and then there's the whole top engine tear down to replace a couple expensive pumps and air valves.

What it is

Brief whirring/revving noise at startup

module and a good read on why/how they fail

Let me know if you have any other questions. I know another member here did the relay/resistor method which works just as well as the module. @superman3043

Bottom line is that you can also just live with it, but it can/will throw codes depending on which part of it has failed and certain codes will throw the vehicle into limp mode (rarest side effect but still a possibility).

It will only activate when the engine is cold. Which is why when you went back out and fired up the truck again it didn't activate. Not sure if you have a scantool or not but might want to do a OBDII scan or stop by a parts store that does complimentary scans. It might turn up a pending code.

Excellent post sir. Will report back after fix

Found it:

http://www.toyota-4runner.org/1398043-post356.html

mine does this too...........guess its normal..opened the hood to confirm, its the fan alright

I read in one of the many searches I did that you could unplug the pump. Where is the plug?