Idle Dips When Brake Pressed

[Ripper]

'85 4R newly rebuilt top end. When engine is warmed up the idle will dip down every 4-5 seconds when I brake. I'm sure it is a vacuum issue but I don't know how to solve it. All my vacuum lines are new. Where do I start?

[jasonmt]

Idle speed is set too high.

[2ndGenToyotaFan]

Ding ding ding!!! Common problem.

[WristPin]

wouldnt say its a "problem" but more of a adjustment needed.

[Ripper]

THANKS!!!!

You guys rock!!

[2ndGenToyotaFan]

Common "adjustment needed" (You think you're soooo great...... boy if I met you in a dark alley......)

[WristPin]

Originally Posted by 2ndGenToyotaFan

Common "adjustment needed" (You think you're soooo great...... boy if I met you in a dark alley......)

no dark alleys in the country

but i might poke you with my poking stick

[WristPin]

your posts are 1234!
05-13-07, 10:58 PM #6
2ndGenToyotaFan
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[beatdown83fj60]

A dip at idle can also be a problem with the brake booster iirc while pressing on the brakes.

[Ripper]

"brake booster iirc"

What is IIRC??

[Blues Dawg]

Originally Posted by Ripper

"brake booster iirc"

What is IIRC??

if i recall correctly?

[beatdown83fj60]

Originally Posted by Blues Dawg

if i recall correctly?

Sorry, Im becoming a nerd in my later internet days.

[Ranski]

Originally Posted by beatdown83fj60

A dip at idle can also be a problem with the brake booster iirc while pressing on the brakes.

I will be chasing down the same issue this weekend. All my research is directing me towards vaccum leak or break booster.

To check break booster do the following:

On vehicle inspection: (before you rip the booster out and yell and scream
at it)

1 check air tightness
- - start engine
- - Stop engine after running for 1-2 minutes

2 pump brake pedal several times.
- -If pedal goes down deep the first time but gradually rises after the 2nd
and 3rd times, it is in good condition. :-)

3 If there is no change in the pedal height when depressed the 2nd and
succesive time it is defective. :-(

Check the operation:

1 With the engine stopped, pump the brake pedal several times with the same
pressure. Ensure that the pedal height does not change.

2 Start the engine while the brake pedal is depressed, place one tablet of
prozacs into the brake fluid reservoir and see if the brakes recover from
their depression. No really, If the pedal goes down slightly at this time,
it is in good condition. If there is no change in pedal height, it is
defective. :-(

Check air tightness under load:

1 With the engine running, depress the brake pedal.

Then stop the engine while keeping the brake pedal depressed.

2 Hold the pedal for 30 seconds. If the pedal height does not change, it is
in good condition. :-)

If the pedal rises, it is defective. :-(