Pulsing sounds near Air Intake Filter? [SOLVED]

Truck: 4cyl 2.7L (3RZ)

Been restoring this truck for the last few months. Doing lots of testing, tuning, etc. Trying to work out this rough idle I have. Recently noticed I have this pulsing sound coming from my air intake filter, which can be heard when putting your head close to the air filter box. It doesn’t change pattern when I throttle the engine. Tacoma’s are new to me so I thought it might be normal until I realized two throttle body hoses connected to the EGR were accidentally crossed causing a p0402. I corrected them, codes went away, truck drove like a dream and the pulsing sound went away immediately. However, next day it came back and I can’t figure out why its doing it or where its coming from. Anyone ever dealt with this pulsing sound before, is it normal?

I’ve tested the whole EGR system (factory manual)
Replaced the IAC & cleaned the MAF
Cleaned the Throttle Body
Tested the Temp Sensor and ECT (all correct resistance)
Completed a Smoke Test, Compression Test, Leak Down Test & Coolant Pressure Test (passed)
Confirmed Injectors are pulsing & have correct resistance
Exhaust Manifold was inspected and confirmed to be sealed

I’m lost as to what part might be causing a pulsing sound or echoing into the air intake filter box.

 

While I have a different motor (v6 3.4L) I was listening closely after replacing my valve cover gaskets & replacing my fuel injectors, and also noticed a "puff puff" pulsing pattern to the air being drawn into the air box. In the stock configuration, there are J traps for catching water, and resonator boxes attached to the intake tube to reduce pulses / smooth out the air flow. Do you have the stock intake, or a aftermarket intake system?

 

Why don't you post a video of it so we can give it a listen? That probably might be the best move unless you have an aftermarket intake, that would somewhat explain the pulsing sounds if you do indeed have one.

 

No codes now correct?

My best guess is the EVAP system purging

 

I have a stock intake. I inspected the J traps and resonator boxes attached to my intake hose but nothing was out of ordinary. Is there something I should be looking for? I did notice the fuel injector system has a hose that connects the air intake, could it be causing this pulsing sound?

 

I can try, but I think the engine is too loud to record the pulsing sound.

 

My comment wasn't as much of a suggestion to inspect the resonator, but more a the intake makes noise to the point where Toyota did something about it.

I don't think the pulsing is an issue.

The vac line that runs "to the fuel injector system" is going to the fuel pressure regulator.

How many miles have you put on the truck after all the items you've listed? Have you reset the ECU since completing those fixes? It might just take some time for your ECU to adjust to the newly cleaned/replaced items.

 

The reason I point out the air hose to the fuel line is because I wonder if the fuel pressure regulator is showing signs of deterioration? As the pulsing sounding does resonate in some form the throttle body/fuel injector area. Obviously sound and vibration travels so its possible I’m just dealing with some resonance, but a rough idle can come from poor fuel/air ratio. Maybe its worth the testing the regulator.

As for the ECU I did disconnect the (-) terminal on the battery but I’m reading online the (+) is better for resetting the ECU? I’ve put roughly 350 miles on it, highway and city. Should be enough to have the ECU adjust, right?

 

[SOLVED] After all that lovely time spent testing and diagnosing. Took it to a diagnostic shop who happened to have an extra and did a swap while testing the throttle body. The IAC out of the box was trash, door was only opening half way.

Never would of known unless I did exactly that. Lessened learned, major engine rebuilds means lots of new parts. Limit how much you swap at once if you can do so!