If you're having air AND fuel spraying out, about the only place that's gonna happen is going to be the injector. If it's just air and "whatever" spraying out of one of the intake runners, it's a valve/valve seat.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)