Got the new ForScan ODB-II dongle but it didn't throw any error codes. Got a cheapo $15 torque wrench and torqued the upper intake manifold plenum down. First bolt, snapped it loose. Got a new, less cheapo torque wrench for $25 with a good Amazon rating. Removed upper intake manifold plenum. Thankfully it was the bolt that sheared so the threads on the captive nut were fine. Called all over town on a Saturday afternoon to find a Ford parts shop with the bolt in stock. Between all the calling and part numbers, I called four different dealerships, each one saying they didn't have it and giving me a different "correct" part number to call the next dealership with. One dealership said the next dealership had it in stock, but called ahead and got it verified that while the inventory system says it was there it was in fact not, lol. Finally, the last dealership said the part number I *really* needed was 5F2Z-9Y450-A. It came in a pack of 4 but they removed two and sold it to me for $2.50 apiece(I wanted a spare bolt just in case).
Removing the sheared bolt was surprisingly easy, went after it with a tissue and screwdriver against a shard of metal sticking up. Removing the upper half of the bolt from the plenum was just a matter of a knock with a mallet. It has a captive sleeve that pops out along with the bolt.
With my new torque wrench and replacement bolt, I popped the replacement bolt into the plenum and torqued it down in rotating sequence as mentioned above(first resistance, then down to 10 Nm (89 lb-in), then another 45-degree tightening). For good measure, also sprayed down the MASS air sensor with some MASS cleaner, let dry and re-installed.
Fired up the engine and the slow, oscillating hum is gone.
HOWEVER, now the engine idles a bit rough. ForScan found no codes. Thinking there is a vacuum issue but all hoses are snug, no hisses, cracks, etc. Also thinking maybe all this jacking around knocked some oil residue loose and maybe a bottle of SeaFoam at my next gas fill-up might help? Could it also be the MASS has to do some mileage to re-learn?
Lastly, I'm not a ForScan guru, quite the opposite, are there some tests I can create/program within it to narrow down potential issues?
Cheers