I have a 2000 Ranger 2.3L with aluminium intakes (upper and lower halves). The truck started idling rough a couple months ago and threw P0171. It's still drivable but idles rougher than normal at stop signs. When I spray starter fluid around the back of the engine on the driver's side, it speeds up. I checked all the vacuum hoses, EGR gasket, and EGR pipe and all were good. I removed the upper half of the intake to check that gasket (which was good) and verified tight bolts mating the lower half of the intake to the head. There isn't anything else on that corner of the engine to suck in air.
Question, would a cracked intake manifold exhibit a rough idle?