There's only one vacuum line that is connected to the brake system: the brake booster. You sure you got it on right? You sure that booster has no leaks? You just described a failing brake booster by your symptoms.

The power steering system might cause idles to drop but wouldn't effect the brakes. Treat these as two issues (that broken valve is probably part of it). This might help: http://personal.utulsa.edu/~nathan-b.../steering.html

The other option is that with the throttle closed, there's still a leak on the plenum allowing the brake booster to pull all the air it wants. But, with a leak that massive I think that your idle would not stay at 800 with no brake applied...

 

i have already replaced the brake booster with a new one and replaced the line on it as well and used new clamps to secure it. I also put on a power steering air control valve and hooked the vac lines to that, still no change, also put on a new plenum gasket on when I had to put on a new valve cover gasket. i've yet to fix the leaking fuel issue until tomorrow since my friend cannot come help today, i went and got new washers today and the seal kit for all the injectors

 

So as you know I've been having the same issue. I finally broke down and took it to a shop. He said I just need to replace my brake booster and it should be all set. Picking up the part tomorrow. Should have it in quick. I'll post an update when I'm done.

 

hope that works for you. I already tried that.

 

Any updates? I too have the idle dip when applying the brakes. I also have been trying to sort out poor brake performance. Truck was purchased a couple months ago with 4 spun rod bearings and lots of neglect. I finished the full rebuild and during the engine breakin i noticed the brakes were horrible.

I have replaced the rear shoes, rear wheel cylinders (one was leaking fluid onto the rear shoes) front calipers, front rotors, front pads (performance friction), front soft lines, pushed a ton of dot 4 through the system bleeding all 4 corners and the LSPV&BV. all vacuum lines (except the large booster line) were replaced during the rebuild.

Brakes are much better but there are still occasional times that the pedal goes hard and increasing pedal pressure does not = increased breaking. I've done my fair share of HPDE and driving schools so I know what brake fade, fluid boiling, loss of booster vacuum (engine stall), abs engagement, etc feel like. This however just feels like the system feezes up when the pedal goes hard. Rear abs is not kicking in and standing on the pedal does not increase braking.

I've been thinking the booster or the check valve in the main booster line is going, or the front piston in the master. The only two symptoms i have at this point are the occasional hard pedal (and no amount of additional pedal pressure increases the braking) and the slight idle dip when pressing the brake pedal at idle.

 

Thanks for the tip, i am waiting on a replacement throttle body (my coolant fittings were so rusted that they broke in half so i had to bypass and then discovered the high idle circuit is driven by the thermowax valve) and will re calibrate the idle settings when i swap the replacement in.

 

I was having the same issue. What seemed to solve it for me was a can of Seafoam in the tank (when half full)'and a can of Seafoam in the throttle body through a vacuum hose.

 

hey everyone sorry i haven't updated. I took it to a shop because I busted one of the bolts on the plenum and finally said ˟˟˟ it and took it to the shop, they fixed that and my fuel rail that leaked and turns out my #1 and #6 cylinders are in the 70's psi range which should be at 120 at least. I decided to put in a rebuilt engine, found one for a good price ($1200) in san fran and had it shipped to my town. it arrived this past friday and should be installed this week. I figured with an engine at 300k miles, might as well replace the thing since it wasn't taken care of anyway. I'll update later when all is done

 

Good luck man!
I hope this fixes your problem

 

hey yall update. new rebuilt block was put in along with a new radiator, running pretty strong now, just have to break in the new engine and keep and eye on the oil, water, and heat. then it'll be time to hit the trails! now it just needs a new exhaust and smog (good ol California), the mech did the knock sensor mod for me too which I didn't know about, and a new clutch pad was installed, quality work by Northside 4x4 in clovis, california