Can a vacuum pump that reads 22 hg at idle still be bad? Yes it can.

I have the same vehicle and experienced the same symptoms you are describing. My problem turned out to be the vacuum pump even though it showed good with the vac gauge directly on the output. After replacing the check valve, the main line from pump to booster and confirming the booster did not leak, i finally replaced my vac pump with a used unit and my problem was solved. I surmise that the original vac pump simply couldn't supply enough vacuum under load.

Easy enough to check the brake booster for leaks though it does take a bit of effort with a mity vac.

__________________
Joe

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1980 300SD - 495k miles - 'The Ambassador'
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Former Family Members
95 C280
73 280SEL
90 300D
87 300SDL (X2)
86 560SEL
84 300D
80 300SD