I'd do a thorough inspection of every vacuum line and fitting. If a hose deteriorates all of a sudden it will allow air in. There is one vacuum line that connects with a plastic T under the throttle body, just above the temp sensor. It runs to the charcoal vacuum canister under the air conditioner compressor. There are at least 2 vacuum lines coming off a fitting at the rear of the upper intake manifold. Then there is the power brake booster vacuum line going from the same fitting to the power brake booster. I'd look at the fitting on the upper intake real close. I had mine off a few weeks ago and that fitting was quite rusted behind where you can't see it well. Look with a mirror, the fitting could have rusted thru and exposed a hole. There is also a vacuum line running to the fuel pressure regulator also, make sure it is tight and no leaking. Those are the lines I can remember.
Anyway, we had a high idle on our 94. Started up and idled at 3000, then very slowly lowered to 1200 or 1150 at the lowest. I tried everything. New tps, new maf, new IAC, sprayed all my vacuum lines down with propane, could not find any leaks. So, I bit the bullet and replaced the lower intake manifold gasket. Bingo, problem solved. it starts at 1200 or so, and idles down to 650 hot. Real nice. If your problem persists for a few weeks, pull all you spark plugs to see if they are burning white, which confirms a lean mixture, or too much air.