OK, I have a 2002 Dakota V6. I have suspected that my Plenum my leak due to a rough idle and seeing some oil in the intake manifold. Inside always looks wet. I blocked off my PCV opening. Blocked off my PCV line to manifold and put a Vacuum gauge on the breather tube that connects to the other valve cover. I followed the Dodge testing procedure and with the engine running my Vacuum gauged remained at or close to Zero. I ran the truck for several minutes and it never increased pressure or created a Vacuum. Could the Plenum still be leaking if the pressure on the gauge doesn't increase. Never even went to 1 psi or went below zero showing a Vacuum.

All the normal tune up procedures have been done on my truck.

Throttle Body cleaned
New PCV
New IAC
New TPS
Map sensor good
New plug wires
new plugs, with proper gap
New cap and rotor
fuel pressure at 50 psi and regulator good
Compression test good
Ignition coil good
All vacuum lines tested for leaks (found none)
New 02 senors (NGK)

If my truck idles for few minutes it will cause the trucks rpm's to drop close to 400 and almost stall the truck. Like if I'm at a red light too long. Truck always idles rough. I was thinking it was my plenum, but my readings have me stumped and I hate taking my truck to a shop.

 

Mine did the same thing. My problem was tracked down to a vacuum idle speed sensor on the back of my throttle body. Did you replace that?

 

Yes, I replaced the IAC.