As long as you don't have any open vacuum connections, this shouldn't affect the idle. You can see if they are open by putting your finger over them with the engine running - you will feel suction if they are open.

I don't have a diagram for an '81 handy, but this may help.

The vacuum for lock/unlock and the climate control system comes from a fitting on the back of the intake manifold. It is low, almost down to the bellhousing. A rubber hose connects the manifold fitting to the plastic line. The line goes to a Y, one side of which goes to the reserve tank under the passenger fender. The other goes to a bunch of Y's on the driver's firewall that split into the yellow (locking), and the green (climate control) lines.

If I had to guess, I would say that the tank connection is leaking so the tank has been bypassed. This is rarely a problem with the tank, it's usually the rubber fitting that seals the hose to the tank. You can get a new one for a couple of bucks at a dealer.

Someone may also have bypassed the vacuum connection to the servo.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe