The injectors are mounted in plastic insulators, these & the idle balance tubes (rubber) should be replaced as well. Over time this type of material gets brittle & that creates vacuum leaks & idle problems

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MERCEDES BENZ MASTER GUILD TECHNICIAN (6 TIMES)
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman
190E 2.3 ITS RACECAR
1986 190E 16V