Idle raises when I pump the brakes hard...?
#1
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Idle raises when I pump the brakes hard...?
I've been dealing with a high idle on my 383 build... the best I have been able to get it is around 950-1000rpm. Today I went out and I just noticed something.....
When the car was parked and idling, I pumped the brakes pretty quick/hard and the idle shot up about 50-100rpm. It would do it when I pressed the peddle down quick, and it would also go up if I took my foot off quickly. What does this mean?
When the car was parked and idling, I pumped the brakes pretty quick/hard and the idle shot up about 50-100rpm. It would do it when I pressed the peddle down quick, and it would also go up if I took my foot off quickly. What does this mean?
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#8
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dude thats totally normal lol...........when u press the brake it uses the stored vacuum to assist you in pedal travel......when you release the pedal the diaphram fills back up with vacuum in the booster........now think about soemthing what is vacuum? lower pressure and the lack of air right? so when you are "filling" the booster with vacuum you are essiantly "removing" the air from the booster.....and that extra air goes into the intake manifold and causes the idle to bump up slightly for a second due to the extra air.......its like pulling off a vacuum line on the intake and then plugging it back in......the idle goes up...........totally normal any car with a vacuum booster will do that........
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Alright cool, thanks for the explanation. I've never noticed it in any other car, it's just way more prominent in this car because the cam is so choppy and the exhaust is dumped.
#12
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Yep. Neither does mine. Unless the engine is not generating any sort of vacuum to begin with, the booster is constantly under vacuum and there is no way in the world pushing on the brake pedal should influence vacuum to the point of altering engine idle. I would venture to say the check valve or the diaphragm in the booster is leaking.
#16
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Easy way to check it is to run the car and then shut it off. Now pull the valve out of the booster. If you hear air rush in then it's fine. It should hold neg pressure for a while so you can run it and pull the valve out like an hour later and it should still be neg charged. or just hit the brakes and listen .
#18
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I reckon it's possible for an engine producing less-than-normal vacuum at idle.
Oh, and OP, you better get a custom cam instead of that 306 because "it's good for nothing more than peak numbers..."
Kidding!
Oh, and OP, you better get a custom cam instead of that 306 because "it's good for nothing more than peak numbers..."
Kidding!