The Vacuum solenoid is activated when the throttle idle switch makes contact, i.e. when accelerating. The solenoid then allows vacuum to the vacuum advance mechanism on the distributor. The only other thing to remember is that until the engine reaches a certain temperature, the vacuum supply goes to the warmup regulator. When the engine has reached temp, the flow of vacuum is diverted by the Thermal control valve (part no 30 page 2.4.0) to the solenoid valve, and on acceleration to the vacuum advance. As to cross over ref, I don't know of a bosch no, but it may be worth you having a word with local Volvo dealer. I'm sure some of the 760 models had emission control on them and the part might appear. I have no idea why it should have been removed but the above might help you decide why. Graham ----- Original Message ----- From: "Martin Gutkowski" <webmaster@xxxx> Subject: [DML] Part X-ref > In overhauling the engine on #2727, we've discovered a part missing. > It's on p2-4-0 of the parts manual, no 27, part 101116 Vacuum Solenoid > Valve part of the "evaporative control system". > What does this solenoid do and is there any reason for it to be removed on an engine with the Island twin kit?