BMW E28 distributor vacuum hoses
Where do the E28 distributor vacuum unit hoses connect?
The canister on the side of the distributor adjusts ignition timing. One hose goes to a vacuum point on the intake manifold and the other to the throttle body: one outside the throttle plate and one inside it. The ports are visible on the throttle body.
Which hose advances and which retards the ignition timing?
At idle there is strong vacuum on the inside of the throttle plate and none on the outside. One hose advances the timing and the other retards it. At idle the timing is retarded and it advances when you press the throttle, so swapping the hoses mixes up the timing.
Where do the other intake manifold vacuum hoses go?
The fuel pressure regulator hose runs between the intake manifold and the regulator. A third hose may go to the interior temperature sensor of the automatic climate control in the lower part of the dashboard. If the distributor hose is disconnected and plugged, the vacuum diaphragm is probably ruptured and the timing control does not work at part load.