Sudden loss of power brake assist

[Boxersix]

Hi guys,

I was stopped at a light and the idle got real lumpy like the car was going to stall, I kept my foot on the gas to prevent it from stalling (about 1000 RPM) then when the light turned I drove off but the first time I applied the brakes the pedal felt dead and it took lots of pressure to make the car stop. I don't know if the near stall is connected to the brake issue or just coincidence... I got to work and shut off the car, I later started it again and the idle is still lumpy and no brake boost.

Any ideas of where I should start looking?

Thanks!
Boxersix

 

[luckymike]

First, I'd check the big vacuum hose from the booster to the engine. Make sure it's not cracked and that both ends are tight. Also check the check valve near the booster end of that hose. If nothing there, I'd guess that the big diaphragm inside the booster has failed. I assume you could check that by trying to draw a vacuum where the hose mounts to the booster.

 

[gsxr]

The 2 issues are likely related. The brake booster needs engine vacuum for power assist, and a rough idle can be cause by a large vacuum leak. Or, something is causing the poor idle and that's causing low vacuum.

Does it drive OK at higher speeds/RPM?

 

[Boxersix]

Thanks guys,
I did some research today and came up with the same ideas. I'll check the vacuum hose and check valve in the morning.
The car does drive fine at higher speeds/RPM.

Cheers and Happy 4th,
Boxersix

 

[Boxersix]

Alright...I couldn't wait until tomorrow to check the vacuum line for a split or hole. I traced the line from the booster back to the manifold. It is kinda buried and probably a bit of a wrestling match to replace. I found where it comes back up to the top of the engine right under the small plastic cover in front of the air box cover. The hex fitting had come undone. All I had to do was reconnect it and snug the hex fitting tight. All good!

I had the car in for a "engine out fix everything" service a few months ago. All the old hoses, belts, gaskets, aged rotating components, oil pan gaskets, engine & trans mounts, flush the brakes, new wheel bearings and other leaky stuff. The tech must have not tightened this fitting properly.

Thanks again for weighing in with your experience. It is so nice to have the 500E Board to run to when I need help.

Cheers,
Boxersix