My 06 Ranger started acting up on the way home from the gym on Thursday. The idle started to become more and more unstable until I had to use the throttle to keep from stalling between shifts and at slower speeds. I managed to make it home, popped the hood and let the engine cool down. I later traced the problem to a vacuum line that had slipped off a nipple on the back of the intake manifold. Once I put it on, I didn't find the connection very tight, so I ended up installing a hose clamp over the slip on fitting to make sure it was fully sealed and wouldn't slip off again. The truck has just shy of 250k miles and the engine's actual mileage is unknown. The engine was rebuilt or replaced by a previous owner.

I didn't take a picture, but the connector I'm referring to connects to the rear of the intake manifold and the nipple faces the firewall, toward the top. It doesn't have a hose clamp and simply pushes onto the nipple. The IM nipple is around 3/8" diameter and the associated vacuum line drops down to a much smaller diameter hose that eventually connects to something on the passenger front area of engine bay, behind and below the headlight assembly. I don't know if this is a common problem, but I thought I would pass it on.