cyl 4 misfire and gulping sound??

2005 Ford Escape 6Cyl, 47,000 miles

Hello all:

The best way I can describe it is a gulping air sound around the intake. it's a deep kind of "woomp woomp" sound. It only happens when the engine is at an idle and ONLY after the engine comes up to operating temperature.

Error codes: Cylinder 4 Misfire Detected & Misfire at Startup first 1000 revolutions

Whats been done so far: Checked vacuum hoses for leaks, replaced all spark plugs (and 6 new upper intake gaskets), replaced coil pack for cylinder #4.

The problem returned immediately with the same error codes. What now? I've been all over the internet looking for the someone with the same problem. I am seeing tons of posts about cyl 4 misfires and rough idling. It seems my situation is unique with the "woomp woomp" sound and it only occurring after vehicle reaches operating temperature and only during idle. The idle seems rough no matter what the engine temp is.

I have a list of things to try but i'd like to prioritize it in the interest of saving money. The list was compiled after much internet research (escapes with similair problem):
-New Fuel Filter
-New #4 Fuel Injector
-Cleaning/Replacing IAC
-Cleaning/Replacing MAF sensor

Any Ideas? I appreciate any help, thanks!