Vacuum issues

I'm getting complete vacuum lock on cold starts about once every 3 to 5 days. Brakes lockup and can't move. Have to warm the motor up then take the hose off the brake booster to release the pressure, which is new along with check valve that's inline.

Any help would be appreciated
V6 motor, 4x4

 

WAG - booster diaphragm may be bad.

To test the booster function once the reserve is depleted. Hold moderate pressure on the brake pedal and start the engine. If the booster is working properly, the pedal will drop slightly.

 

Tannis,
I have the same issue with my 95’ 4Runner. Two new boosters, new check valve. It will be fine for a week then start doing it. Mine will also do it on warm days if I turn off the motor and then turn it back on in about 5 minutes. Totally baffled. Did you solve your problems? Sure would like some help. Thanks

 

I have the same issue with my 95’ 4Runner. Two new boosters, new check valve. It will be fine for a week then start doing it. Mine will also do it on warm days if I turn off the motor and then turn it back on in about 5 minutes. Totally baffled. Did you solve your problems? Sure would like some help. Thanks