Brakes and boost

What do they have in common I see that we have a line coming off the return plenum that goes to the brake booster. How does this function? Does it suppy the vaccum for the brakes? When I get I real bad idle I cannot depress my brakes at all. I have better braking it seems whe the engine is off.

I am currently investigating the vacuum assist for the SC brakes..

The master cylinder is mounted to a canister that sits against the firewall. This canister is the power booster, and uses vacuum applied to a large diaphragm to amplify pedal pressure. It can fail causing reduced or no assistance, but can not increase pressure.

It sounds like what you are experiencing is an increase in pedal effort. What model year is your SC? If it is the Teves mark II system, you may have a failing accumulator. Are any brake lights on? Also, how does your idle misbehave?

I have a 95, the brake lights do come on. My idle is only bad after a hard accel. THe thing is though before the car idles bad the brake pedal gets really hard. Then it will idle down to about 400 then kick back up to 1500 and so on, until it dies. Meanwhile my boost gauge will be at 0 to 5psi.
Thank you for any help

Have you made any progress on this issue? I can not logically connect your brake behavior to the idle problem, but it sounds like you could have a vac leak. You might also have a failing IAC.. do you hear goose honking noises or similar at shutdown?

check the innercooler tubes for leaks. mine would barely idle and if i touched the gas it would go way up in rpms and then drop to nothing almost and cut off, no check engine light. i had it apart and didnt tighten the upper connection at the innercooler. it sounded like the altenator bearing had gone bad,loud whinning sound. i tightened the connection and it cleared right up. also read in here that the big nut on the upper cooler line will come loose. i never touched the brakes though so i may be way off.

No more progress, I took it out agian I dont have a leak. I finally got an engine code but have yet to get it checked. It idles fine all of the time until i go above 10lbs. I have had a few vac leaks before and it would not even let me boost that much. At WOT im above 15 I have not checked the pipes but it is not acting like it is a leak. It only happens after I let off the throttle.

93 and up SCs require vacuum for the brake booster to function correctly. How much ?...I'm not sure, but I know a couple guys who had agressive cams that lowered the vacuum to around 10 inches at idle and had problems with the brakes just like what you are describing.

I would suspect a vacuum leak (possibly in the brake booster) is what's causing your problems with the idle and the brakes.

David