RPM's drop when brake pedal is pressed

[acslater9]

Sup guys I have a 91' 240sx with a ka24de engine in it.

Anyways, like the title says when I press my brake pedal while standing still AND driving it drops my RPM's to about 500-550. Here's the weird part though, When I have my car on park my RPM's are at 800-900. As soon as I go from park to drive (automatic transmission) the RPM's drop to about 700-750. Then when I go and brake it drops to 500-550.

I don't know the problem I heard it might be a vacuum leak but I have no idea where the hell to check it. So that's why I'm posting this here so I can get some help. :)

[Purestock240]

vacuum issue

[acslater9]

Can you go in depth into how I can resolve this issue? Thanks

[brndck]

Vacuum leak at the brake booster or the vacuum line to the brake booster. Inspect all components, and with the car running, spray brakekleen or starter fluid on these components. If there is a leak, it will suck the brakekleen in and the idle will kick up momentarily.

[yetijeff]

FYI normal rpm for an auto is 750, manual is 700. Just noticed it on my hood sticker the other day lol

[zerodameaon]

^Yup that's what it should be in park, and idle down when shifting into gear is normal, shouldn't be much though.

[acslater9]

Thanks for the info. Would a cracked hose leading to the brake booster be a cause for the vacuum leak? I ask that because I have it on my hose. :eek3:

[jaxshawn]

yup, make sure to replace it with a strong hose so it does not collapse under vacuum

or just order the oem check valve it comes with the hoses i believe and last time i checked it was around $15-20

[acslater9]

yup, make sure to replace it with a strong hose so it does not collapse under vacuum

or just order the oem check valve it comes with the hoses i believe and last time i checked it was around $15-20

Cool thanks, when replacing that hose will any fluid come out?

[unwtdhero]

Yeah gas will so use a lighter to dry it up.... Just playing, vacuum hoses only contain air.

[acslater9]

Alright so I went to autozone and they said they don't have the rubber hose that goes into the brake booster. Any other places that you guys know that sells them?

[Rich260z]

It just needs to be vacuum hose in the right sizing. As long as it's flexable and you don't pinch it in a bend it should work. Measure the OD of the booster outlet and ask for like 4ft of that size line.

[acslater9]

Thanks so they should have it in Autozone? And its called Vacuum hose correct? Also whats the OD of the booster? Sorry I'm new to all of this. :)

[Alamo_City_210]

Outer Diameter. or just take the old hose with you.

[acslater9]

Thanks to all those that helped out I fixed the cars idle early last night.

Now if you could all try and help me on my next problem! here the link.

http://zilvia.net/f/s-chassis/535450-car-won-t-start-cold.html

Thanks.

[Frank_Jaeger]

Alright so I went to autozone and they said they don't have the rubber hose that goes into the brake booster. Any other places that you guys know that sells them?
Nissan sells them for about $40 I think. Ask me how I know.

You really don't need a molded hose. Just get one with the same ID and OD.