Usually, the Exhaust Manifold warps and takes the intake
manifold with it causing a vacuum leak. Since it's fuel
injected, there's no chance of the old "rich-in-the-center"
cylinders. At least once a year, you should check the
torque on the exhaust/intake manifold bolts. The same
fasteners hold both of them on to the side of the engine.
The weight of the 2 manifolds hanging off the side of the
engine, and the expansion and contraction of a nice cool
intake manifold and very hot exhaust manifold cause the
gaskets to fail. There's a couple of ways to fix it: Replace
the Intake/Exhaust gasket and have the two manifolds
milled together for a flush fit and replace all of the
fasteners OR go aftermarket (if you can still find them) and
get separate manifolds - preferably with a Stainless Steel
Exhaust manifold or Header.
2 people found this helpful.