Pulating idle with brakes applied

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R

ray299

10 Year 15 Year
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Jan 6, 2007
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Ok, the whole reason I'm doing all this work to my truck in the first place is that when the brakes are applied, the idle pulsates. When sitting there in teh driveway by itself it'll idle fine. Its only when I step on the brakes that the irradic idle will show itself... Anyone have any ideas???
 
Check the TPS, it is very fussy. Then check your timing, and finally set the idle speed screw on the throttle body to the spec idle speed (650, I think).
 
Sounds like you may have a brake booster going bad. try shutting the truck off, let it set a minute or so then hit the brakes. If the pedal is rock hard right away, the diaphragm in the booster is more than likely bad. Since it idles good at all other times, I would be willing to bet on the booster. Good luck!!






Ian Campbell
 
too high of idle will cause the ecu to kill the injectors with the brake switch activated.
it is used in a decel cycle, desinged for when your moving.

so adjust your idle.
use a 8mm wrench and a 3mm (maybe) allen/hex wrench.
loosesn, adjust and tighten the screw/nut on the thottle linkage.
set it to 850 rpms

also the dashpot is some what adjustable. but only do so if is whats causing high idle.

and dont F with the big slotted screw on the throttle body.
its got yellow paint on it.
 
and dont F with the big slotted screw on the throttle body. its got yellow paint on it.[/QUOTE said:
You're right about the high idle causing the ecu to momentarily reduce fuel supply while the brake is applied, but...
I think you might have the only idle adjustment screw with paint on it...the screw is the normal and recommended(by the FSM) way to adjust then idle speed.
Click to expand...
 
Pluton said:
You're right about the high idle causing the ecu to momentarily reduce fuel supply while the brake is applied, but...
I think you might have the only idle adjustment screw with paint on it...the screw is the normal and recommended(by the FSM) way to adjust then idle speed.
Click to expand...

the 2 options i described do adjust idle speed.


when the other two prescribed adjustments do not suffice, then turn the screw. If you have a FSM, its outlined in the MA section.

850 22RE auto
750 22RE manual
 
I take it you have EFI... when my 22re did this... i tried everything and nothing worked until i noticed in the fsm and chilton manual that there is a wire coming in to the ecu that is described as brake s/w... every time you push in the brakes... your brake light switch under the dash sends a signal to the ECU for some type of decel cycle as mentioned by Wristpin and pluton. What i did is carefully pull that lead from the main plug that plugs into the ECU.. so when the brake light switch is engaged... that signal doesn't make it to the ECU that causes the fluctation in idle. This may be the cheap way out or the cheap way of fixing things but it worked for me. Dont unplug your brake light switch though... you won't have brake lights.
 
toyotology said:
I take it you have EFI... when my 22re did this... i tried everything and nothing worked until i noticed in the fsm and chilton manual that there is a wire coming in to the ecu that is described as brake s/w... every time you push in the brakes... your brake light switch under the dash sends a signal to the ECU for some type of decel cycle as mentioned by Wristpin and pluton. What i did is carefully pull that lead from the main plug that plugs into the ECU.. so when the brake light switch is engaged... that signal doesn't make it to the ECU that causes the fluctation in idle. This may be the cheap way out or the cheap way of fixing things but it worked for me. Dont unplug your brake light switch though... you won't have brake lights.
Click to expand...
Thanks! I'm gogin to try that next... The TPS is dead on... the truck is still apart because I'm looking for a fault with the knock sensor. I keep getting a code 52 (knock sensor/ecu) The ECU, sensor and wires seem to be all good though... I'm stumped...
 
Yota Tony said:
Sound like a vaccum issue to me.
I know on my old trail rig when I had a vaccum leak and hit the brakes the truck would stall out.

Check for a vaccum leak and then check the brake boost and master cyl.
Click to expand...

I htought so too... I checked the master cyl and put all new vaccum lines on.... no difference...
 
death_engines said:
Its the TPS. Had this problem on my 87 4runner. I couldnt get it to adjust, so I just took it off. that was 3 years ago. Ran fine ever since...
Click to expand...

TPS we are talking throttle position sensor. There is now way in hell you can just take it off.

The idle issue, what happens when you turn the a/c on at idle and apply brakes?
 
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