When I apply the brakes my idle drops too much
 

My 350 SBC (mild cam, turbo 400) idles fine, at about 900 RPM.

When I apply the power brakes in PARK, the idle drops about 200 RPM.

When I shift the automatic trans into, DRIVE, or REVERSE, my idle drops an additional 150 RPM, or so, which I believe is probably normal.

It is at this point, the idle, is down to about 550 RPM, and the idle becomes rough, barely running, but does not stall.

I know that is not electrical, as I have completely removed the ALL wiring from the vehicle.

The only electrical wiring left is the ignition switch, with 3 wires.

Any thoughts

Re: When I apply the brakes my idle drops too much
 

Your booster is likely leaking somewhere.

Re: When I apply the brakes my idle drops too much
 

Anybody else ??

What is the best way to test the booster?

Re: When I apply the brakes my idle drops too much
 

Mity-vac or plug it.

Re: When I apply the brakes my idle drops too much
 

I'm assuming you have a vacuum power brake booster. Must have a vacuum leak.. either in the booster itself or possibly in the vac line or connection? Disconnect the vacuum line, plug it and see if it makes a difference in the idle.

Re: When I apply the brakes my idle drops too much
 

I was also thinking vacuum leak. But could it be the torque converter?

Re: When I apply the brakes my idle drops too much
 

Like the others have said, power brake booster.

Re: When I apply the brakes my idle drops too much
 

O.K. s the latest.

I disconnected the vacuum line to the booster and plugged it, idle remained at 900 RPM.

When I applied the brakes, NO decrease in RPM, so, I'm guessing that the booster is a problem, but when I shifted into DRIVE, the RPM dropped to about 575 RPM. about where it was previously, with the booster connected.

I'm at a loss, someone mentioned torque converter, can that affect idle?

Re: When I apply the brakes my idle drops too much
 

How are you setting idle? What screws are you using, the idle mixture at the carb base or the single one at the throttle?

Re: When I apply the brakes my idle drops too much
 

It is a brand new Edelbrock 1906 carb with an electric choke, I am NOT a seasoned mechanic, but I adjusted the (2) screws at the base of the carb, with a vacuum gauge to get the best vacuum.

The screw on the right side seemed to do little, but the best vacuum I could get was 15-16 inches.

Then I set the idle screw to about 900 RPM

Re: When I apply the brakes my idle drops too much
 

Set your idle when hot at 750 rpm.
Then check your initial timing.
If it’s below 10 degrees bump it up to 14 degrees. Plug off vac advance line doing that.
Check your idle is at 750 again.
Adjust your mix screws.
See how that works.

Is your vac advance hooked to ported or manifold vacuum port?

Re: When I apply the brakes my idle drops too much
 

I don't have a timing light, I am using ported vacuum.

Re: When I apply the brakes my idle drops too much
 

If you’re gonna get it running right you need a timing light.
A digital or dial back type works.

Or you could set the timing like I learned to 50 years ago.
By ear!
Advance it until it pings, back it off a touch. Lock it down, adjust idle down to a guesstimated 700 and test drive.

Re: When I apply the brakes my idle drops too much
 

Two weeks ago I gifted one like this to a new mechanic in training.

https://www.summitracing.com/parts/s...iABEgLe8vD_BwE

Re: When I apply the brakes my idle drops too much
 

Harbor Freight has a cheap one with dial back feature, worked great for me.