After replacing my stock intake with an AEM Brute Force intake and a 'throttle body spacer', all seemed fine. After a few weeks, I began to notice a transient 'bubbling' sound that seemed to be coming from the air filter end of the intake. This has gradually intensified over the months, but does not seem to cause a major performance issue (and no DTC). The engine idle speed is affected though, and dips down to around 500 RPM before returning to normal, and then it randomly starts again, each day, every day.
After removing the air filter and holding a feather at the end of the open intake, it was obvious that when this 'bubbling' sound accompanied by the RPM change was occurring, that air was temporarily not being sucked in and the engine was starving for a few moments. When the bubbling sound stops and the engine idle goes back up to 700 or so, the feather would indicate a good, strong vacuum at the filter end of the intake.
I have (very) carefully cleaned the 2 sensors that are in the unit, but can't seem to remedy this. I should mention that I have a Hypertech program installed, and that uninstalling/reinstalling make no difference.
This intake hesitation and idle issue have intensified, and are more noticeable in 'cold' weather than in hot, here in Tucson, AZ.
I'm at my wits end. I hope I've described this in such a way that someone can help me with some good advice. Thank you!!!

 

The IAC controller is varying the air bypass opening.
This directly controls idle speed.
Be sure the IAC is clean and not sticking.

 

Thanks for the advice. Forgive my ignorance, but I don't know what IAC stands for (internal air...?) . Also, can you tell me where it's located?

Much thanks,

Howard

 

I.A.C.Valve- Idle Air Control Valve. Located on the rear of the intake , on the passenger side , near the firewall. Possibly your problem. It could also be the filter. These trucks are very sensitive about the air intake. I would also take a look at the throttle body and make sure the butterfly isn't carboned up.

 

I will check those things out. Thanks a lot!

Howard

 

Thanks again for your help, SteevenH and Bluegrass 7. I unbolted, removed & cleaned the IAC. The hesitation and sputtering went into brief remission before returning, for the first time in 4 years. I'll call this a victory once I replace the part.
This forum is a great resource, and I'm grateful for the expertise and time. HGB

 

Sometimes cleaning is not the end and it needs to be replaced.
The IAC is a spring loaded plunger/piston device that may have an issue where you can't get to.
The PCM 'pulses' the piston under spring pressure to open it, then the spring pressure pulls it back when the pulsing is less.
This is how the device controls the amount of air that bypasses the throttle plate to control idle speed.
The idle speed is actually a small range of numbers in a software table in program.
The crank sensor reports the crank RPM to the PCM, that in turn opens the IAC to 'find' an rpm match with the table value and settles in that position with small amounts of corrections to keep the idle close to 750 rpm +/- a small amount.
That isn't the end of it, to go a little farther; on a cold starts the IAC is opened wide, idle is set higher due to the input from a coolant sensor until the motor warms or is brought down by control from a software timer in the program.
The OX sensors also get into the game.
Good luck.

 

It was quite the fiasco getting the part from Holmes Tuttle Ford here in Tucson, but I finally received a new IAC valve & gasket yesterday. I installed it as soon as I got home from work (the parts dept. supervisor felt so bad about my order that he had a driver deliver it there and discounted the price of the part), and that is the end of the erratic idle and associated 'bubbling' sound coming from my intake.
Thanks much; my baby purrs again!