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The mkiv Supra Owners Club

Why does holding the brakes lower rpm?


RedM

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Jspec auto TT.

 

I've noticed that, when I'm at a standstill (or sometimes when crawling in traffic), pushing the brake pedal down fairly firmly causes my idle revs to drop below my normal idle speed.

 

Normally the car idles at a tad over 500rpm but I can drop it to about 480-490 when on the brakes.

 

Normal and/or to be expected?

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when you use your breaks, you use power, and and your putting stress on the auto box

 

its a bit like "why does the revs change when i press the A/C button"

 

But when you press the A/C, the revs go UP slightly, or when you turn your lights on, the same happens. Very strange for the revs to go down!

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I think mine idles at 500 because I have the 'stealth' option enabled.

 

your car idles at 500 rpm? QUICK get it to a garage there is something really wrong with it!!!!!!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

you are a bit paranoid about your car :p :D :d

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When you press the brakes you use vacuum boost assist, which is taken directly from the intake plenum. This means a bit of air that was going into the engine doesn't any more, so the idle drops slightly. It's only noticeable at idle because of the relatively small volumes of air involved.

 

The idle going up when you turn on the aircon is electronically controlled - the ECU pumps up the idle control valve to compensate for the realtively large load the aircon compressor puts on the engine.

 

Try turning the steering wheel at idle as well, or putting on the rear demister - these too up the idle ;)

 

-Ian

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