I can offer a couple of suggestions. First check the check valve. When you pull it out there should still be plenty of vacuum in the booster a minute after the engine is stopped. Check for vacuum leaks. If none are found, measure the vacuum at the check valve. 19 to 20 inches of mercury is normal. If it's low you might do a compression test to determine the engine condition. If the idle speed needed to be bumped up in the past there is going to be less vacuum. Check for a collapsing hose too.
If you installed a used booster, there were some that used two diaphragms inside. One could be bad giving the false impression it's working. There were also some that must not be laid down without a special cone in place to hold an internal valve in place. If a used booster is bounced around and that valve pops out there won't be any power assist.
Jun 10, 2013 at 11:10 PM
