High idle

[Brian]

I have a 1998 ford ranger 4.0 liter v6 4X4, the idle is real high when I first start it but then settles down after a couple minutes of running.There is no check engine light on but I noticed bad mpg and when the idle is settled down it still has a higher rpm to the point if I let go of the gas pedal the truck can move on its own.I also have a hissing sound coming from the brake pedal area the sound goes away when I press the brake pedal I do have one wheel cylinder that is leaking that i haven’t repaired yet, one more thing when I turn on the temperature control knob to put AC or heat on the air only blows out of the defrost vents no air comes out of the other vents I’m telling you all that I think might be a related thing altogether

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[Arthur Fieser Jr]

Sounds like you have a blown out seal in your brake booster causing you to have a vacuum leak. A pretty major vacuum leak at that if your vent selector isn’t working. I’m almost positive this is what it is from how you described it but a way you can test it is to go under your hood and remove the vacuum line going into the brake booster and just plug it up with your thumb or something to restrict the flow of air, and see if that fixes your idle problem and have a buddy check your vent selector to see if it works while you have the line plugged. Sorry if i jumbled any words up, just woke up 3 minutes ago, haha.

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[Arthur Fieser Jr]

[IMG]http://uploads.tapatalk-cdn.com/20160505/9305dbada65e86b9f08ca7b102770e6c.jpg[/IMG]
Here is what the vacuum line going to your brake booster will look like, if your brake booster is leaking then the engine will be running pretty lean because it is sucking extra air in and it can’t compensate extra fuel for the extra air because the leak is past the map sensor, or maf whichever your vehicle has. So you definitely want to get that fixed asap because running lean will hurt an engine due to higher cylinder temps.

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[Brian]

Thanks for the reply it looks like the brake booster was repaired from the previous owner it looks new to me, could it be possible that the vacuum leak is leaking from the check valve you are showing me in the picture because I’m not sure where the brake booster seal is.

[Brian]

I just did that test you told me about it did help the idle a little but it still is high he rpms goes up to almost 2 then after running for about a minute it settles down, when I had my son put his thumb on the hose when I took off the check valve on the booster it did stop the hissing sound from the brake pedal and the pedal felt better when I pressed it down so your test did help maybe fix one problem but the high idle is still there and the vents didn’t work

[Arthur Fieser Jr]

Well the vents not working is definitely a vacuum leak.

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[Brian]

Here are some of the codes I got from autozone today p045 ,p0171 ,p0174 I looked under the dash following the brake pedal to where the brake booster goes in the fire wall feel air leaking out of the rubber boot area, is there a seal there or something.I just bought this truck from a private owner couple weeks ago it wasn’t doing this when I test drove it and took it home.The brake booster appears to be almost new.I’m lost on what to do I read that the blend door actuator might be bad and on this truck it’s behind the glove box I took it out and left it unplugged and it wasn’t turning so maybe the blend door actuator might be bad

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