[12Ounce]

BACKGROUND: A few years back, when my '99 had approx 60k mi, the DPFE sensor had to be replaced. At 90k mi, the infamous P0171 & P0174 also showed up. The conventional wisdom of the day was "replace all gaskets and seals on upper and lower intake manifolds, and replace the LH valve cover".
CONDITIONS FOUND: There was a little fresh oil on top of the "spacer". The lower intake manifold, including the IMRC butterflies, was a gooey mess. Was this condition worsened by the earlier EGR problem? Very difficult to clean. The EGR jets were all fouled ... a couple were completely plugged.
ACTIONS TAKEN: Cleaning done and recommended replacements/repairs made. NOTE: The improved "green" isolator bolts were not then available. Taking note of how the "upper" was actually a loosely assembled clipped together two-piece part, I decided to use some sensor-safe RTV to better support the inside piece. In fact, the "upper" inside part was RTV'd to the "spacer" .. around the six air horn connectors. This experiment may have had an unintended/unexpected good impact.

CURRENTLY: The '99 now has 160k miles and is beginning to pre-knock under load. No codes yet. I decide to do the intake manifold repairs again with the new green isolator bolts, and also replace the long overdue plugs and serpertine belt.
CONDITIONS FOUND: Much more oil found on the "spacer" ... perhaps a few ounces. However, the "lower" was surprisingly clean. No goo. The IMRC butterflys almost as clean as when I earlier left them. Almost NOTHING in the EGR jets ... not enough to dirty a pipe cleaner. Apparently the applied RTV successfully sealed the "spacer" away from the "lower", preventing the oil from leaking down onto the intake manifold runners and causing the gooey residue. ???
ACTIONS TAKEN: All ribbed o-rings and isolator bolts replaced. All bolts torqued (10Nm) in two-step sequence per Haynes manual. All old RTV peeled away from the six air horn connections and connections re-RTV'd. Don't know for sure if the RTV was important, but why take chances. (I wish I knew how to insert a digital image here. ???). New double-platinum plugs and belt. Winney runs great again! The plugs were probably causing the pre-knock, but I'm glad to get rid of old black isolator bolts ... though I didn't see any seal loss... they would have eventually caused a problem.

TIP OF THE DAY: Do not leave Haynes manual outside overnight if rain is expected.