Just to echo @db4690, I had to replace the intake gaskets on my Ford Explorer to solve a recurring lean burn code. The gaskets I pulled out looked good, but replacing ythem eliminated the problem.
On my Supra, I had to pull the plenum to get to the plugs and the gasket kit they gave me was wrong. Put it back together with the old gasket, and it started hunting for idle, a classic vacuum leak symptom. Got the right kit, installed the gasket, and idle returned to normal. Both kits were inexpensive Felpro, and worth every penny.