State the procedure for checking a vacuum operated brake servo

Possible vacuum operated brake booster problem. Make sure adequate supply of vacuum is at the booster. If vacuum and booster are ok, possible seized caliper slide pin assemblies/seized wheel cylinder/s or defective ABS control unit if equipped

Sounds like the vacuum servo is faulty. Atmospheric pressure should only be applied to the back side when the pedal is pressed. Seems like the valve must be leaking? Make sure you have a little free play at the pedal also.

I wonder if you have an air leak in the brake servo? Check the manifold vacuum as you operate the brakes. Look for bad hoses around brake servo.

The vacuum is created via a mechanical pump driven from the cam, Or a separate, electrical pump.

The only liquid I have ever found in any servo (booster) is brake fluid from a leaking master cylinder.
If the vacuum is low/absent, due to a faulty cam driven vacuum pump, and crankcase pressure rises, along with a faulty one-way valve in the vacuum plumbing, it's possible the oil could be forced into the servo housing, and operating the brakes would help it happen as the servo could act as a pump itself and draw oil from the engine.

Found some diagrams:
http://www.jimellissaabparts.com/showAssembly.aspx?ukey_assembly=408206&ukey_make=1032&modelYear=1999&ukey_model=14675

http://www.eeuroparts.com/Cars/SAAB/41962012/2009-9-5-Aero-Wagon-2-3L-4-Cyl-16-Valve-Turbo/1019/Front-Brakes-Hydraulics/

What colour is the oil?

Check the condition of the pads, disks, and operation of both. They should be freely moving.Also check that your brake lines are free of air and that your fluid is clean.
Also check that the vacuum line to your brake servo is intact, and that you have adequate vacuum to your servo.

Check condition and operation of idle control valve.
Also check condition of vacuum lines and brake vacuum assist hose and vacuum assist servo.

To check if you have a vacuum leak before the servo unit, first check hoses and connections, then pull off the vacuum hose to the servo unit and put your thumb on the end of it. You should feel a strong pull/vacuum. If you release your thumb then you should hear the engine revs climb, and then possibly go back to normal.
If you feel lack of vacuum, then you likely have a leak somewhere.

Another thing to check is that when you pump the brakes several times, the engine note changes and your brakes become stiff for a second or two before becoming softer again.
After you have run the engine for a few seconds and then turned it off you should be able to pump the brake pedal three times, with it being soft-ish each time until all vacuum has been spent from the servo unit, and then your brakes become stiff again. If this seems not to be the case, and they are still all the time, then you have a vacuum leak, possibly in the servo unit.

your power brakes have a vacuum operated part in them that makes power brakes "Power" this part has failed, it is called the power brake booster, u will need to have it replaced see picture below, it is under the hood driver side.

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check for vacuum pump operation - remove pipe at vac pump and check for sucking on end of finger, check pipework to brake servo unit for chafage / disconnection. if no vacuum at pump replace the pump ive had a few like this

hi from uk you do not say if engine is petrol/diesel ? reason for asking is that on petrol engine the vacuum for b/servo is from inlet manifold whereas on diesel it is created by a seperate vacuum pump usually on uk models by being bolted/driven on the alternator by belt ? however from what symptoms you describe i would suspect that on 1st application on brake pedal ? the vacuum is gone hence pedal goes hard due to loss of vac assistance ? whereas vac should last for 2 or 3 applications ?b4 all vac is gone when vehicle/engine is off so the problem may be the vacuum hose to servo unit is leaking or split ? or the servo inner piston diagphram is leaking as you press pedal resulting in no assistance unfortunately servo is not serviceable and req's replacement this is not beyond diy if you wish to? on diesel vacuum is from pump but same principle as to vacuum for servo this may be pump thet is worn out ? or hose split ? or on some occasions thedrive belt slack? also on some diesels the vac pump can be driven off therear of camshaft ? in which case pump considering age of car +milage ? may be pump fault SO hope you understand all above? try this run engine then stop press b/pedal and if pedal goes hard or slowly pushes back ? this is vacuum being used and leaking you can test pump with vacuum guage then check if operating and holding good vacuum if not pump is worn if yes then may well be servo diagphram you can buy servo units without the b/master cyl which you will not require

Check for vacuum leak within power brake servo unit.
Remove vacuum hose from brake servo and block off the open vacuum line from the engine. Check that engine then runs normally when brakes applied.
Do not drive the vehicle with the vacuum servo disconnected, as the brakes may not be effective. - The pedal pressure required to apply the brakes effectively may exceed your capabilities.

If the brake booster servo diaphragm is leaking it will need to be replaced/repaired.