Try pinching off the vacuum hose to the booster and see if the engine runs any better.

Answered by Wrenchtech (expert)
14,716 answers provided

The diaphragm in the booster can leak while still being able to help apply the brakes. You can verify it is leaking by observing the brake pedal right after you stop the engine. It should hold vacuum for at least two power assisted applications long after the engine is stopped. If the pedal gets hard to push as soon as the engine stops, either the booster or the vacuum check valve is leaking. To test the check valve, pinch the vacuum hose going to the booster while the engine is still running. Now if you have two or more power assisted stops, replace the check valve.

It's more likely to be the booster because the check valve dosn't do very much while the engine is running and it won't cause rough running. Only the booster has to be replaced. If you don't unscrew any of the steel lines from the master cylinder, you won't have to bleed the air out either.

Answered by caradiodoc (expert)
17,274 answers provided

The most common area for vacuum leakage for Toyota vehicles would be the brake booster to master pump push rod seal. The seal is held by a spring clip and removing the master cylinder holding bolts and pulling the master cylinder slightly away from the booster would enable you to visually inspect the seal. Too bad there are no service parts available so the booster has to be replaced as an assy.

Answered by KHLow2008 (expert)
39,832 answers provided