Pumping Brakes and Diminished Idle

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just-rust
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Pumping Brakes and Diminished Idle

Post by just-rust »

Today I was sitting in my car while it was idling. I noticed my "Stop Lamp" light was on and pumped the brakes to see if I could get it to go out. While doing this I noticed my idle would drop to the point where my engine would stutter, almost as if it was going to die. When I would stop pumping, idle would level out.

I know the brake booster draws vacuum to assist the brakes. In a situation like this would it draw enough to offset engine operation? I didn't look to see if vacuum decreased but will check tomorrow.

I am thinking there is a reasonable explanation but haven't been able to find one. I also have video of this happening if anyone is interested.
Rusty 1991 EJ22T - VF28 - '07 wrx TMIC - MBC - Invidia DP - Walbro 255 SOLD
1992 Legacy SS 5mt, with some neat stuff on it
Legacy777
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Re: Pumping Brakes and Diminished Idle

Post by Legacy777 »

Yes, if you continually pump the brakes the brake booster's vacuum draw from the engine could produce the drop in idle you described.
Josh

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just-rust
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Posts: 233
Joined: Thu Dec 26, 2013 4:22 pm
Location: Minnesnowda

Re: Pumping Brakes and Diminished Idle

Post by just-rust »

Thanks for the response Josh. Just wanted to make sure that was normal.
Rusty 1991 EJ22T - VF28 - '07 wrx TMIC - MBC - Invidia DP - Walbro 255 SOLD
1992 Legacy SS 5mt, with some neat stuff on it
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