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There is a very common problem on this engine with vacuum leaks between the middle intake plenum and the lower intake manifold. These leaks, however, tend to be present ONLY when the engine is cold, and will be worse during cold ambient temperatures. Ford has revised parts to cure the problem, consisting of new "isolator bolts" that bolt the middle plenum to the lower intake, and new "port gaskets" (o-rings) between the middle plenum and lower intake.
2. If using a smoke machine to try to prove this, it usually will not show any leakage unless the engine is stone cold. Also, some leakage from the Exhaust Gas Recirculation (EGR) valve, the Idle Air Control (IAC) valve vent, and the Intake Manifold Runner Control (IMRC) levers IS normal. Potential Causes: Leaking Intake - cold. There is also a TSB for this problem as well.
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