Popping noise in intake

[rayner601]

I have a popping noise in the intake. It happens when you let off of the throttle after revving the engine from idle to about 1200 RPM. It isn't a backfire sound just a gentle thump you can hear in the air filter housing. When it does this, the IAC also buzzes. It will also let the idle lope about 300 rpm and the IAC is buzzing then as well. Cleaned IAC, plugs are autolite platnum gapped at factory specs with about 15k on them, fuel pressure is 30 at idle, 35 under load, 35 with regulator hose unplugged. I am leaning towards a fuel pump and or IAC. Any help is appreciated.
Joe

 

[1969350]

"It isn't a backfire sound just a gentle thump you can hear in the air filter housing"

"Damn.. I noticed the same thing today with mine...been chasing a problem with the
engine stumbling after warm-up and driving a bit. Losing MPG and power , had a fuel pressure gauge on motor and noticed that 'popping ' sound on occasion and especially after reving it also. Can even hear it at idle sitting in car with door open if you listen. That's when I started looking for source of noise after waiting for idle to come down and warm up a bit.
I just put in all new platinum plugs air filter and coil boots recently. But never heard this
before. Engine is not idling as smooth as that 4.6 DOHC should idle. Started swapping coil packs again with spares to see if it would stop. No difference on bank 2 have to get to bank 1 this week on day off. Have to check my fuel pressure this week while driving also. Hate to replace anything that doesn't need replacing...yet!