one addition that made a dramatic decrease in underhood temp and the hot engine idle on my 300se /90 was the installation of a heat insulation wrap on the exhaust manifolds down to the first joints.
the temp stays at around 80 "C instead of 100C during the very hot months. A/C also is super cool due to lower temp. As the underhood temp is low at switch off the injectors should stay cleaner (lower heat soak).

mak