Strange idle issue

- A
- ag2ward
  
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posted
20 years ago

Thu, Nov 27, 2003 6:07 AM

'89 Toyota pickup, 207K miles

Weather just turned cold - temp 15F - 40F now and this issue may be related or just a coincidence.

The issue: When I press on the brake, the idle revs up and slows down rhythmically. The frequency is two to three times in a five second period for as long as I keep my foot on the brake. As soon as I remove my foot from the brake, the idle returns to normal. The operation of headlights has not affect on this, nor does blinkers, heater, fan or any other electrical function (to my knowledge).

It is so noticable that it is almost embarassing at intersections. Sometimes kids next to me think I want to race them and I get funny looks. (For this reason, I take my foot off the brake whenever possible.)

Any help is appreciated. TIA

AG2

- B
- bearman
  
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posted
20 years ago

Thu, Nov 27, 2003 3:45 PM

Could be the brake booster which uses engine vacuum.

- R
- Roger Brown
  
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posted
20 years ago

Thu, Nov 27, 2003 5:57 PM

Check out this site:

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The root cause of the problem is that the idle speed is set too high, turn it down under 1000 RPM (should be around 800) and the idle will be steady with the brakes applied. Logic is that the ECU cuts the fuel injectors if the RPM is above about 1000 RPM and the brakes are applied; assumes you are braking to a stop, so why keep feeding fuel to the engine.