940 Non-Turbo

When I continuously pump the brake pedal, the rpm drops and then up in sequence with the pumping action.

My car is suffering from a low rpm bouncing syndrome, meaning rpm needle keep bouncing always between 400 to 900 rpm. At times car shudder because of sudden drop in rpm

Is this a sign of a failing booster, causing a vacuum leak?

I am suspecting this because my toyota does not have this symptom when I pump the brakes.

Thanks for the inputs.

Laozong

Also check the vacuum hose from the power booster. Exhaust heat causes cracks that a casual inspection will not reveal. You need to bend the hose back on itself to reveal cracks.

Life expectancy in a turbo for that hose is about 9 years, for normally aspirated it is longer.

Take care,
John H from Downunder

Thanks John for the response.

Checked out the booster hose. Look clean and relatively new to me and no leak.
Would it be a conclusive test if I were to remove the hose at the throttle housing and plug the vacuum nipple to see if the rpm continues to fluctuates?

Thanks & Regards
Laozong

I'm experiencing the same problem with my '93 945T (I posted a similar question a couple weeks ago). The answer I got was that it's likely the brake booster vacuum check valve. That's good news, because you can get one at FCP Groton for less than $10. I haven't ordered mine yet, so I can't report back with a success story. But at least you have some place to start.

Jeff Pierce
--
'92 Mercedes 190E (my daily driver), '93 945 Turbo (a kickass family car), '53 Willys-Overland Pickup (my snow-plow truck/conversation piece)

Jeff Pierce, Thank you for the information.

The booster hose looks good to me and the check valves, white in color seem rather new. I suppose my mechanic would have replaced that without my knowledge and there was a whoosh sound when I unplug the valve. THe valve blows only one way so that rules out the valve.

If you come across any more info please let me know.

Thanks and Regards
Laozong