Idles fine until you tap brakes

-
C

carcrazyguy

Well-Known Member
Joined
Feb 5, 2005
Messages
1,358
Reaction score
16
Location
Amarillo, TX
I am guessing it has something to do with vacuum? The car is a stock 318 2bbl and it idles fine until you touch the brakes. Then it idles rough until you let off the brakes. We thought it might have been in the power brake booster, change that it still did it. Put the original booster back on and checked carb lines. Still have not found anything. Any suggestions??
 
Sounds like a bad vacuum booster., or maybe the check valve. Just saw you changed booster, was it a new one or used?
 
It was from a parts car. What is the best method on chasing a vacuum leak? It would have to be the carb vacuum lines, the booster or a leak under the dash lines that go to the heater/ac controls, right?
 
try disconnecting the booster-- plug the line & see what happens--- try it before the check valve & after the check valve---- if it works fine -- you then have narrowed your problem down, Lawrence
 
carcrazyguy said:
It was from a parts car. What is the best method on chasing a vacuum leak? It would have to be the carb vacuum lines, the booster or a leak under the dash lines that go to the heater/ac controls, right?
Click to expand...

I would definitely try a known good booster.
 
VDART said:
try disconnecting the booster-- plug the line & see what happens--- try it before the check valve & after the check valve---- if it works fine -- you then have narrowed your problem down, Lawrence
Click to expand...
I agree...plug all vacuum sources....you may not be creating enough vacuum to use the booster....things that change it are too big of a cam and poor idle mixture setting...put a vacuum guage on the intake manifold and see what kind of vacuum you are pulling at idle...I would think that you need 14 to 16 lbs of vacuum at idle to run that booster..
 
VDART said:
try disconnecting the booster-- plug the line & see what happens--- try it before the check valve & after the check valve---- if it works fine -- you then have narrowed your problem down, Lawrence
Click to expand...

Brilliant suggestion.

Good luck.
 
Blocked off the booster (and at the manifold). Now when you tap the brakes it does not change the idle. Now I need to find a new/replacement booster.

I doubt the cam is large enough to create this issue. It is basically an E58 360 cam.
 
You must log in or register to reply here.
-

Back
Top