Possible partial brake booster failure?

[1997chevydriver]

Ok guys, I have noticed during these extremely cold (for my area) temps that i think my brake booster is failing.

When i push on the brakes if I push a little over half way, i hear/kinda feel a "thump" then my idle fluctuates. during this time, if i hold it, i hear what i believe is a vac leak.

If I hook up my torque pro app, the short term fuel trims support my vac leak theory by ******* out at 50%.

If I move my foot (letting off) about an inch it stops, idle returns to normal and STFT return to normal.

The odd thing is if it's relatively warm (0°+) it won't do it.

So I guess my question is, can brake boosters partially fail?

 

[1997chevydriver]

Bumpity for day crew

 

[SAATR]

Considering that it's supposed to hold vacuum under all conditions, I would just call it failed. The rubber may have become a bit dry rotted over the years and the cold reduces its elasticity even further , causing your leak when it's very cold, but sealing again when the temperatures rise and it becomes more pliable. Dump it!

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[1997chevydriver]

Ok that's what i figured. Gonna wait till it warms up a bit and I can get it in the garage