Y29 is a switchover valve to control a shift delay on the transmission when cold. Y30 is the overboost protection switchover valve. If the sensor on the manifold trips from an overboost condition it is supposed to vent to atmosphere to prevent fuel enrichment (essentially cutting boost due to no ALDA enrichment).

If you have a copy of the service manual, it should have the wire colors noted for each plug.

For what it's worth, I run neither of those valves on my car. The shift delay is supposed to help warm up the catalytic converter faster. Federal diesels have no cat, so it is a pointless item, it just made the 1-2 shift excessively high/late/sloppy when cold.

The overboost valve is one that's a bit more controversial. A lot of people feel that it's important for safety of the engine should the wastegate fail. Clearly it was installed for a reason, however given the inefficiency of the engines lacking an intercooler and the IP already being pretty well maxed out on a stock tune at 14PSI boost, I don't lose sleep at night without mine in the circuit. My switchover valve was seized up, so it was never going to vent to atmosphere anyway.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

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

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]