Vacuum leak from intake manifold O-ring gaskets on Mercury Mountaineer

Problem Description and Possible Solution

The intake manifold O-ring gaskets commonly leak, causing stalling and poor idle quality; the Check Engine Light will illuminate.

Problem Data
RepairPal Verified
Average mileage: 135,160 (14,000–235,000)
Engines affected: 4.0L V6, 4.0L V6 SOHC, 4.6L V8, 5.0L V8
8 model years affected: 1998, 1999, 2000, 2001, more2002, 2003, 2005, 2006
33 people reported this problem
Viewing 1 - 10 of 10 comments
Rough Idle and throwing engine codes p0300 random engine misfire. Before replacing gaskets I bought 2 new coil packs and new wires and plugs (performance) spent about $275 and still had problems like no other. Buying gaskets now and putting them on and its fixed
Vehicle shuts down at an idle or a slow speed or at a stop sign have to put in n and it starts right back up
had valve cover gaskets changed,the mechanic had to remove intake to do this,he replaced upper intake gaskets and since this has been done my mountaineer has a misfire type sound,it idles rough,check engine light is on and it gave a code for camshaft sensor,changed that and still having same problem.