I would have to agree there is unmetered air entering the intake when the metal to gasket surface is cold. When the metal absorbs heat is will "seal" the vacuum leak and return to the correct air/fuel mixture.
A likly culprit may be a leak in the fuel rail to intake manifold seals. They become hard with time and fail to seal the fuel rail to the lower intake manifold, causing unmetered air to enter the head. My O2 sensors are seeing this lean condtion and causing an erratic idle and slight buck at highway speeds. When the correct operating temp is reached the vacuum leak is eliminated. Hence, the air/fuel mixture is perfect and drivability problems cease to exist.
I am wondering if anyone else doing a complete UIM/LIM system rebuild see a specific gasket failure that was causing an intermittent lean code? The 95-97 duratecs are the only motors w/ the fuel rail to intake manifold seal.
Or if the problem was with an injector o-ring? I was trying to search for some posts that had some pics of the gaskets that were replaced.
Has anybody had this similar problem? And what did you find the problem to be?
Last edited by a95dohcLS; 12/11/05 03:12 PM.
1995 Mercury Mystique LS OBD1
2.5 L Duratec ATX- No modifications
70,000 Miles w/ O.E. Water Pump
or
Replaced: VSS, Lower speedo-cable(2X)
Use: Mobil 1 5w30 and Techron Fuel Treatment.;) and
Mobil 1 ATF Change every 10,000 miles
