NOTE: This is a brief summary based on my experience and loosely on a Ford Technical Bulletin. Most of our SVOs have or are beginning to accumulate many miles. As time goes on the rings, valve guides and turbo seals start letting more oil film by them. When this gets excessive the throttle body, upper intake, vane air meter and rubber hose between the vane air meter and turbo start to collect oil deposits that can and do cause the troubles listed above. Excessive oil accumulation in the air intake hose to the turbo can even cause detonation.
So what do we do about this sludge and varnish that is where it shouldn't be? Your first step is to get a couple of spray cans of a good quality carb cleaner (Ford officially suggests using Ford carburetor tuneup cleaner rather than carb choke cleaner) and a stiff long handled bottle brush. If things are really bad it wouldn't hurt to buy a throttle body to upper intake gasket, an upper to lower intake gasket along with an idle air bypass to throttle body gasket, a TPS and EGR gasket.
Remove the intercooler and check it's hoses for hardness and cracks. Remove the vane air meter to turbo hose and check for cracks, tears or excessive hardness. A coiled wire should be inside this hose to prevent it from collapsing. I suggest that you tape up or cover the turbo inlet and outlet to prevent nuts, bolts, tools and small pets from being left behind to be later boosted into the engine. Using the carb cleaner, the brush and rags, clean and dry this hose out. Follow the precautions listed on the carb cleaner. Prolonged contact can irritate your skin and the fumes are somewhat strong.
Then hold the throttle open and inspect the throttle body, especially around the throttle plate. If it is not too dirty use the brush, rag and some carb cleaner sprayed on the rag and brush to clean it. DO NOT just start spraying carb cleaner into the throttle body--it will end up in the lower intake and your cylinders. Don't get carb cleaner into the TPS or idle air bypass valve. The same procedure can be used to clean your vane air meter on the car. Again just don't start spraying into it as there are sensors and related electronics in this unit. The vane can be carefully moved with your hand to get at things better.
Let's say your throttle body and upper intake are really bad, what do you do then? Start by getting out your manual and follow the steps to remove them from the engine. This will involve some time and care. After you have said bad words about loosening the tube nut to the EGR (use care as these are no longer available), disconnecting the TPS and idle air bypass connectors, and the nut and bolt arrangement that holds the dipstick support brace to the upper intake, take a break!
Being really careful not getting the carb cleaner into the TPS and idle air bypass, give the throttle body a thorough cleaning. If you don't trust yourself, then remove the TPS and bypass. Try to scribe the exact position of the TPS on the housing to avoid having to re-adjust it for the correct outputs. I have had luck with disassembling and cleaning the idle air bypass, but if it looks really bad and you're reaching the end of your patience, head for your Ford parts counter. Then remove the EGR valve from the upper intake and clean the upper intake completely. EGR valves are another story. If yours look like the inside of a grease pit, take it in hand and make the trip to Ford. There is a code on the EGR that is needed to replace it with the proper part. Your local parts store will not have one. The vane air meter also can be removed for more complete cleaning--just follow your manual and keep the cleaner off the areas that contain electronics.
After another break, follow your manual and put everything back together. You will say some new bad words about the parts mentioned above because your hands now have some new nicks and scrapes that really hurt when you get them again. Double check the fit of all the hose clamps and that the air passage hoses are completely over the fittings. An air leak will not be appreciated by your computer.
There you are, all finished! You've saved yourself a bunch of money and your SVO should again run like new. Clean up, put your tools, and manuals, etc. away and go for a country drive. It will be more fun with your SVO running right again.