I have a 1999 Rav 4 2.0 4dr 2wd. It idles rough when stopped with my foot on the brake. If I put it in neutral or park it smooths out. I've been told it's the power brake booster not holding vacume. Wouldn't I have brake problems too? If it is the brake booster is it the only part that would need to be replaced?
Try pinching off the vacuum hose to the booster and see if the engine runs any better.
May, 21, 2011 AT 10:40 PM
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.
May, 22, 2011 AT 3:50 AM
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.