Re: What to check on a 1999 E350 EB 160000 miles 5.4 engine
Other than the plug issue, there isn't that much that goes wrong with these vans that's particular to them. The radiators don't last forever (but are cheap enough), and other stuff may have been abused, so I'd take a look at all the fluids. I'd be suspect of any fluids that are obviously new, but not overly so, some folks will in fact simply change them to get the vehicle freshly serviced and ready for sale.
There's lots of information out there on general pre-purchase-inspection, do a search and you should find plenty.
160k miles is far from the end of the life for an e-series, but any number of things may be due. If they are, look up what they take to sort, and negotiate the price based on that. -- In both buying and selling cars I've ended up knocking off about 75% of worst case costs and have so far come out under that to actually take care of whatever needed sorting.
'99 EB ex ENG KSWB news van, low rent 4x4 conversion (mostly fixed by now), home built interior.