97 Dx Revs when Brake is Realeased?
03-30-2017, 01:29 PM
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97 Dx Revs when Brake is Realeased?
Car: 1997 Honda Civic Dx 5 Spd, stock.
So I just jumped my car and let it warm up and all that and sat in the car ad accidentally pressed the brake while I was putting my feet down. Dx's dont come stock with a rpm gauge but I could clearly hear the engine rev another 2-300 rpms because my hood was still up. After slowly pushing in the brake and letting out a couple times I started increasing the pace and the rpms would go higher and higher (it wasn't red lining or anything but maybe getting up to 1.5-2k). I did some research and a couple people said its normal with a vaccum brake booster? I just wanted to clarify that and see if its true or not. They suggested to put my hand in front of the intake tube and if it kept running that means theres a vaccum leak, should I do that or am I in the clear? Thanks for any help in advance.
So I just jumped my car and let it warm up and all that and sat in the car ad accidentally pressed the brake while I was putting my feet down. Dx's dont come stock with a rpm gauge but I could clearly hear the engine rev another 2-300 rpms because my hood was still up. After slowly pushing in the brake and letting out a couple times I started increasing the pace and the rpms would go higher and higher (it wasn't red lining or anything but maybe getting up to 1.5-2k). I did some research and a couple people said its normal with a vaccum brake booster? I just wanted to clarify that and see if its true or not. They suggested to put my hand in front of the intake tube and if it kept running that means theres a vaccum leak, should I do that or am I in the clear? Thanks for any help in advance.
03-30-2017, 02:46 PM
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03-30-2017, 06:28 PM
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Re: 97 Dx Revs when Brake is Realeased?
That is normal, because the brake booster operates on engine vacuum. The air used to "recharge" the power brakes goes into the intake and makes the rpm temporarily increase.
03-31-2017, 05:20 AM
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Re: 97 Dx Revs when Brake is Realeased?
03-31-2017, 08:17 AM
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Re: 97 Dx Revs when Brake is Realeased?
The ECU is supposed to watch the brake switch signal to compensate for this. Chances are your IACV is just getting slow/laggy with age. Even though the ECU changes the IACV voltage to briefly compensate for the expected fluctuation, the IACV isn't quick enough to react instantly. Of course a new IACV is VERY expensive purchase to attempt fixing such an extremely minor issue.
BTW: While their are cheap Chinese knockoff IACVs out there, most of the big-brand IACVs are just re-boxed OEM Denso units. The Duralast one I purchased at Autozone was an OEM Denso. Even had the OEM Quality-control markings on it. And although the new one I bought was quicker to react than my original, I couldn't justify the high cost so I returned it (plus it didn't change high-idle startup issue). Autozone now offers online-purchase coupons too, so there are deals to be had. And they will always accept those item in return at the local store.
BTW: While their are cheap Chinese knockoff IACVs out there, most of the big-brand IACVs are just re-boxed OEM Denso units. The Duralast one I purchased at Autozone was an OEM Denso. Even had the OEM Quality-control markings on it. And although the new one I bought was quicker to react than my original, I couldn't justify the high cost so I returned it (plus it didn't change high-idle startup issue). Autozone now offers online-purchase coupons too, so there are deals to be had. And they will always accept those item in return at the local store.
03-31-2017, 10:41 AM
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Re: 97 Dx Revs when Brake is Realeased?
The ECU is supposed to watch the brake switch signal to compensate for this. Chances are your IACV is just getting slow/laggy with age. Even though the ECU changes the IACV voltage to briefly compensate for the expected fluctuation, the IACV isn't quick enough to react instantly. Of course a new IACV is VERY expensive purchase to attempt fixing such an extremely minor issue.
BTW: While their are cheap Chinese knockoff IACVs out there, most of the big-brand IACVs are just re-boxed OEM Denso units. The Duralast one I purchased at Autozone was an OEM Denso. Even had the OEM Quality-control markings on it. And although the new one I bought was quicker to react than my original, I couldn't justify the high cost so I returned it (plus it didn't change high-idle startup issue). Autozone now offers online-purchase coupons too, so there are deals to be had. And they will always accept those item in return at the local store.
BTW: While their are cheap Chinese knockoff IACVs out there, most of the big-brand IACVs are just re-boxed OEM Denso units. The Duralast one I purchased at Autozone was an OEM Denso. Even had the OEM Quality-control markings on it. And although the new one I bought was quicker to react than my original, I couldn't justify the high cost so I returned it (plus it didn't change high-idle startup issue). Autozone now offers online-purchase coupons too, so there are deals to be had. And they will always accept those item in return at the local store.
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