If i pump the brake pedal while ideling the rpm's drop dramatically. why?
#1
If i pump the brake pedal while ideling the rpm's drop dramatically. why?
If my 83 S is idleing at like a stoplight or something and i pump the brakes the rpm's drop off almost below the bottom mark on the tach, if I pump then hold the pedal down the rpm's stay that low and the engine spits and sputters in an attempt to stay running. Does this mean i have a vaccum leak or what? I tried pumping the brakes at idle on the TA and the rpm's go up. I assume thats what is supposed to happen. If anyone can shed some light on this problem i would greatly appreciate it. TIA
#3
yes, vacuum leak at the break booster. pretty common my car does the same thing. nothing to worry about considering the fact that locating the leak is almost impossible.
do the lights dim also? how about when you run accesories such as heat and A/C? You might have a weak alternator or battery.
do the lights dim also? how about when you run accesories such as heat and A/C? You might have a weak alternator or battery.
#4
Old [Sch|F]ool
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Sounds like your engine's running a little too lean at idle.
It's normal for idle to change when you PUMP the brakes. That's how vacuum boosters work - it's a diaphragm with vacuum on both sides. When you push the brake down, you allow air (from the passenger compartment, incidentally, which is why it makes a pssh noise) onto the back side of the diaphragm and this helps push on the master cylinder. When you let off, the valve closes and another one opens to equalize the vacuum on both sides of the diaphragm.
So when you pump the brakes, you're basically using the vacuum booster as a foot-operated vacuum leak.
It's normal for idle to change when you PUMP the brakes. That's how vacuum boosters work - it's a diaphragm with vacuum on both sides. When you push the brake down, you allow air (from the passenger compartment, incidentally, which is why it makes a pssh noise) onto the back side of the diaphragm and this helps push on the master cylinder. When you let off, the valve closes and another one opens to equalize the vacuum on both sides of the diaphragm.
So when you pump the brakes, you're basically using the vacuum booster as a foot-operated vacuum leak.
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#6
Thanks for the replies guys. So is there something i can adjust/replace/fix to make it not drop so dramatically? The only reason i really asked this to begin with is, on a cold day, when the engine is warm enough to kick the choke off, but not fully warmed up, just pushing the brakes, and disengaging the cluch (i.e. stopping at a stop sigh) causes the car to die instantly. Once it warms up for another few minutes its fine. Thanks
#7
Originally posted by Suparslinc
yes, vacuum leak at the break booster. pretty common my car does the same thing. nothing to worry about considering the fact that locating the leak is almost impossible.
do the lights dim also? how about when you run accesories such as heat and A/C? You might have a weak alternator or battery.
yes, vacuum leak at the break booster. pretty common my car does the same thing. nothing to worry about considering the fact that locating the leak is almost impossible.
do the lights dim also? how about when you run accesories such as heat and A/C? You might have a weak alternator or battery.
![Smilie](https://www.rx7club.com/images/smilies/smile.gif)
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#8
Beware Of Squirrely Wrath
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82Transam said:
You're supposed to take it out of gear before you let it out...
j/k
BrianHeston
just pushing the brakes, and disengaging the cluch (i.e. stopping at a stop sigh) causes the car to die instantly
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BrianHeston
#10
You might also try hitting it with the timing light. I had a really bad problem with idle until the car was completely hot. Would constantly die. She was a few degrees off, once I adjusted it, she doesn't stall out when cold anymore.
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