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Underbody braces, turbos and more!

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PostPosted: Sat Mar 14, 2015 2:39 pm 
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Joined: Sun Apr 07, 2013 4:01 am
Posts: 87
Location: AZ
I've been experiencing this intermittent problem with my idle. My normal 800rpm idle vacuum is usually about 19-20 psi steady needle and brake idle up works fine. But every once in a while at idle with my foot on the brake the vacuum drops 3-5psi to 14-16 psi and car idles rough at 3-400 rpm. If I let my foot off the brake, the vacuum comes back up. If I pump the brake the vacuum will drop further with each pump down to 10 psi. I checked the VSV valve (ign off vs on w/ headlights) and it tested fine. I removed the hose to the brake booster and it's in good shape (no gunk or deterioration) and the check valve in the hose works fine. The brakes work fine as well i.e. the pedal never goes stiff. I original thought the check valve or VSV was the culprit, but now I'm wondering. Anybody seen this before?


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PostPosted: Sat Mar 14, 2015 8:51 pm 
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Island Inbreeder
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Location: Emerald city Washington
what
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edit this post had no relevant to OP's question....jv&s
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All turbo cars First maintenance I do is Check an clean sensor ground on the intake plenum
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Last edited by jaguar,vettes&sprints on Mon Mar 23, 2015 10:55 pm, edited 2 times in total.

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PostPosted: Sun Mar 15, 2015 10:05 am 
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Joined: Tue Oct 19, 2010 9:16 am
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Location: sidney, nebraska
I have seen similar symptoms occur shortly before a vacuum booster failed. It was on an old ford my dad had. It would idle fine until use stepped on the brakes and had the pedal in "that one spot." Push past it idle was fine, back off same thing. About a month later there was a constant hissing under the dash, the booster diaphragm had ruptured.

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PostPosted: Sun Mar 15, 2015 3:19 pm 
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Joined: Sun Apr 07, 2013 4:01 am
Posts: 87
Location: AZ
aqqus wrote:
I have seen similar symptoms occur shortly before a vacuum booster failed. It was on an old ford my dad had. It would idle fine until use stepped on the brakes and had the pedal in "that one spot." Push past it idle was fine, back off same thing. About a month later there was a constant hissing under the dash, the booster diaphragm had ruptured.


Thx! Yea, this is kinda what I was thinking or that the check valve was sticking. Temp's in Tucson are around 80+ here in the day and goes to high 50's at night and I noticed that this is happening mainly at night the last two days. I drive all day and never see it, even with the headlights on in the day time. But last two nights it started to do it 2 + hours after sundown.


@jaguar,vettes&sprints- appreciate the reply, though my car is the Turbo + has EFI .


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PostPosted: Wed Nov 11, 2015 2:13 am 
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Joined: Sun Apr 07, 2013 4:01 am
Posts: 87
Location: AZ
Well I drove all spring & summer and this problem was maybe seen once a month if that. I checked the check valve again and it seemed maybe, sticky, but functional five out of six tries i.e.blowing both directions once. With winter coming and cooler nights the problem resurfaced almost nightly last week and my brake light would also came on now but disappear after the car warmed up. So I ordered a 3/8th Aluminum check valve off ebay http://www.ebay.com/itm/like/131555790258?rmvSB=true and took out the old hose at night and it tested bad i.e. air blows both ways. Hit the hose on few objects, at the inline check valve location, and could get it to function again. So I replaced the hose splicing in the new check valve and the problem of vacuum drain with pumping the brakes is gone. Vacuum stays steady and the engine has gained a bit of it's demonic torque back as well. Probably wish I did this back in March but thought the whole PB booster was gonna go then.


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