Brakes causing engine to drop 600 RPM

[KDXSR5]

Ok, I have a problem. When I step on my brakes, my rpms drop 600 rpm. It is idling at 1400, and it will drop to 800 when I push on the brakes. If I keep my foot on the brakes, my rpm will jump from 800 to 1400. Any ideas?

[KYOTA]

vacuum leak

[KDXSR5]

A leak on the hose to the booster? or just anywhere? Maybe my booster is rusted and leaking vacuum? I think when I drop in my engine I am building, I will get rid of all the unnecessary vacuum and emissions stuff to simplify things.

[jimbo74]

idles @ 1400? isn't that kinda high?

[79coyotefrg]

i say either the booster line  or the diaphram inside thew booster

do you hear a hissing sound  when you mash the brakes??

[KDXSR5]

idles @ 1400? isn't that kinda high?

Thats how high it high idles, normal idle is 1000, its always been that way.

i say either the booster line  or the diaphram inside thew booster

do you hear a hissing sound  when you mash the brakes??

I don't hear anything when I push on the brakes... hell I barely feel anything, my brakes have problems.

[79coyotefrg]

i would replace the booster  and then use a  Marlin fj80 master

[jimbo74]

Thats how high it high idles, normal idle is 1000, its always been that way.

so it only does this at high idle when cold?

[93tonkatoy]

The idle adjustment screw is on the left top of the throttle body. Turn the screw clockwise until your idle drops below 1000. Then, see if the brake still causes the idle to drop. If you get the screw turned all the way in, and the idle will not drop, you have a vacuum leak SOMEWHERE between the throttle and the head. To narrow it down, start by pulling the vacuum hoses off the manifold one at a time and plugging/capping the hose/barb. !!! DO NOT FORGET !!! Check the compression joint in the egr pipe between the egr valve and the connection to the intake. Tighten the nut as tight as you can. If this is loose, it will cause a large enough vacuum leak to make it impossible to set your idle. Whatever system causes the idle to drop lower (or the engine to die when you plug the port) will be the offending system. Check that whole system closely, and replace hoses/fittings as necessary. It could also be as simple as a vacuum line disconnected somewhere (probably a small diameter one).

If the computer sees that the engine is above 1000, and you press the brake, the computer turns off the injectors until the engine speed drops to just above idle speed (engine braking), then it turns the injectors back on, so it will continue running.

I've been through this right after I got my truck, got all kinds of suggestions on what it was, but the egr compression joint leaking was the problem I had.

[KDXSR5]

WOW so much info!! Thanks, I will look into it next weekend, I have the rest of this weekend filled with stuff. It only does it sometimes, and this is the first time I could actually connect the problem to something. It doesn't matter if hot or cold, and sometimes my truck idles at 1400, sometimes 1000, and sometimes it drops to 800 and runs like crap. When at 800 and I rev it up, black & white smoke shoots out. I am pretty sure I have a blown headgasket.

[93tonkatoy]

If your head gasket is blown (between water jacket and cyl.), you would be losing coolant. To check for that, WARM the truck up (not HOT), and carefully remove the radiator cap, then watch the opening for bubbles. You would see bubbles coming up out of the coolant, and or, not be able to keep the radiator full (will push some coolant out, then a big bubble, followed by the coolant level dropping way down.) Also, when you first start it up, you may get some splatter (coolant/water and the black soot) out of the exhaust.

Black smoke means you are running rich. Somewhere, your ecm is not getting correct info about how much air is being taken in, and is sending too much fuel to the cyl's. several things can cause this, from the AFM to the temp sensor or the cold start time switch. Dig into the FSM and test all of your sensors. http://personal.utulsa.edu/~nathan-buchanan/93fsm/  They are usually the cause of the little pain in the butt problems.

[GJToyotabug]

hey what if your truck starts idling under 400 all at random?

[porkchop]

hey what if your truck starts idling under 400 all at random?

You got problems

[GJToyotabug]

well my truck idles at about 1000 RPM and then it will drop down to 400-600 RPM so I'll turn it off and turn it back on and it will idle fine

[tryn2Crawl]

Its that white valve that runs between the hose  which runs from the manifold to the booster...If it idles and drops if you step on the brakes then thats what it is.

I'd even put money on that......Change that and you're good....Recently had that problem on my cousins rig.....Idles fine now....

[79coyotefrg]

well my truck idles at about 1000 RPM and then it will drop down to 400-600 RPM so I'll turn it off and turn it back on and it will idle fine

need more info grasshopper

what year truck

[GJToyotabug]

1991 toyota pickup 22re

[93tonkatoy]

the correct idle speed is 700 - 750 rpm.

hey what if your truck starts idling under 400 all at random?

I would make sure your idle stop screw on the throttle has not vibrated out. that sounds like your throttle is not stopping in the same place every time.

[GJToyotabug]

OK I think I fixed it my idle screw was all messed up it's a good thing I have a complete extra intake!

[KDXSR5]

awesome

[GJToyotabug]

now I need to replace all of the vacuum lines like I told myself a month ago

[KDXSR5]

haha, yeah... my vacuum leaks are so bad I can hear them whistling when I rev the engine. It sounds like I have a turbo spooling underhood.

[GJToyotabug]

yeah mine has a bad exhuast leak I need to pick up new seals from my friend and my extra head.