Did I find a vacuum leak?

Whether the engine has a carb or fuel injection, if you block the air intake it should stall, correct?

With the air cleaner off (and no open vacuum ports) on my Dakota, I can completely cover the throttle body (tpi not tbi) and the idle won't change one bit.

I did the plenum gasket upgrade when I first got the truck, but have always questioned how good a seal I got on the intake..

Not overly familiar with the TPI stuff but it may get its idle air from somewhere other than the main throttle body. Block it off real good, start it, and hit the throttle. Bet it dies

Heck, I own it and I'm not overly familiar with it..

While I did completely cover the top, I didn't try to wing it. I'll give that a try tomorrow.

Reason for looking in the first place is that the truck is running ever so slightly rougher and the mileage has dropped a bit.

open the throttle body and look down the intake,if you see oil the plenum gasket is fubar

the IAC valve is where it gets air for idle till the butterfly's open. you can block the round hole at butterfly's but it will idle on IAC port which is about the size of the end of finger. plunger pulses to meter air for idle. mass air flow/ throttle position sensor/ intake air temp sensor/ coolant temp senor/ idle air control valve all need checked for a ruff idle high fuel consumption

look for a small open hole around the opening for the butterfly's.

the plunger on the IAC valve will get pitted and carbon build up. check the first gasket under the valve body to make sure small passages on TB are not carbon plugged. this can cause a ruff idle.

check for oil on bottom of plenum.. you know the fix there already.