STRAZZE93

so heres my problem.. when the engine is cold and i drive my truck around and come to a stop the idle is fine. but thats probably because its still trying to warm up..
when the engine finally warms up and im driving ill start pressing on the brake and slowing down and the rpms slowly drop to about 400 which causes the whole truck to shake and feels like its about to stall out. when i lift my foot off the brake the rpm needle goes up by about 100
i really do not know what to do. ive messed with the idle many times and the idle doesant seem to stay consistant. sometimes its at 900rpm and sometime it just chills at 600.
but the part that is making me mad is stepping on the brakes and the whole car shaking like crazy. i dont know why the rpms drop so low when coming to a stop.
please help im going crazy..

Inferno451

There's no way we can help you unless we know what you're driving. You could be in an 87' supra swapped 4runner, a 79' 20r truck, or a 2012 v8 tundra. We need at least the model year, what kind of vehicle, and which engine.

STRAZZE93

i edited the "my rig" but its not showing for some reason.. sorry
i have a 1990 4runner 22re 5spd 190,000

corich

The brake booster runs on vacuum assist. I'm wondering if the diaphragm in your booster is bad, which means that applying the brake exposes the engine to a major vacuum leak (it's a huge hose) and messes up the mixture, causing it to run rough? A check for that would be to start the engine with the brake pedal depressed - if the pedal gets softer after the engine starts, your booster is working right and my theory is junk.

There are also some little VSV's (vacuum switching valve - vacuum/EFI interface doodads) that boost idle speed when power accessories are adding load to the idling engine - I'm not sure if there is one for the brakes though. If there is, you might check to see nothing's wrong with it (bad wires, cracked hoses...)

I'm kind of new to these rigs -- just got mine a few months ago, so this advice is barely worth the paper it's not printed on, but I hope it helps.

STRAZZE93

i just tried that and the brake peddle did not get soft or anything it stayed firm

MaK92-4RnR

^^ exactly. the Brake booster is vacuum assisted. my truck is starting to show signs of fatigue. yours is just closer to going out.

STRAZZE93

my brake booster is close to going out?

corich

If the brake pedal doesn't change its feel at all when you start the car, that means that engine vacuum is not getting to the booster (bad crack in the hose? hose accidentally disconnected?) or that the booster has already failed, I'd say. I'm guessing it takes some leg strength to stop the truck lately?

STRAZZE93

well when you push the pedal when the cars off it gets stiffer just like it should.. when you start the car it will feel softer because the brakes have power now right?
its been doing this since i bought the truck in october of 2011

masterbasch

I have the same/similar problem. I don't think mine is break related, I think it somewhere in the EGR system. Replacing my EGR valve did not fix the problem but when I unplug the vacuum hose that's on the top if the EGR valve the problem goes away. You might want to try that to see if you have the same problem as me. I don't have I fix for it tho. Could be VSV but I haven't looked into it yet. Here is a link to where I've been posting my problems. Im still tying learn how this stuff works myself.

https://www.yotatech.com/forums/f116...w-idle-248883/

angrybob

These guys above regarding the brake booster are right. With the engine off, pump the brakes until the pedal gets hard. Start the truck and one of two things will happen:
1. pedal gets soft - booster is working fine
2. pedal stays hard - booster needs to be replaced

That's it. If #2 then replace the booster and you should be fine. Some advice though - I would rather take my chances with a bone yard Toyota booster than a new reman'd one...especially for the price.

TylerH

I know this is random but are you low on coolant. I have the same problem, truck runs fine when cold but gets warm and idles low. If your coolant is full and theres no leaks i would rule that out.

Anything above 70 degree weather my truck does it really bad. like idles almost around 400 till i give it gas again.

STRAZZE93

No I am not low on coolant. I'm going to try and unplug the EGR line today and see what happens I'll let you guys know

nothingbetter

Don't waste your time with the egr. You already know what the issue is! Its your brake booster. You did the test, posted the results on here, we figured out your problem. Now replace it! (we arn't doing that for you, but we may give you tips)

STRAZZE93

no the brake booster is fine.. the car was off i pumped up the brakes until they were hard and then started it up and they became soft like they should..
i also unhooked the egr vacuum line and it also did not help with the problem.. idk where to go from here..

old fart

I just went through this yesterday, after messing with my maf yet again. I'd press my brake, rpm's would drop, get that shudder and shake, let off the brake, it'd idle up, and smooth out. Our 2 local yardf mechanics started in on my truck, and found that the larger rubber hose that goes from the brake booster to the intake, although attached, was loose, and or not created a good seal. They loosened the clamp, shoved it on tighter, tightened the clamp back up, and my problem was fixed. So brake pedal pressed, it never dropped below a grand on the rpms. Hope this helps.

SoCal4Running

How long since you did a basic tune up?

Including new spark plugs, new filter (air), change ALL vacuum hoses (it $10 worth of rubber so no whining ) and adjusted the valves.

4Crawler

iTrader: (3)

What is your idle speed set at?
- http://www.4crawler.com/4x4/TLCA_Tru...ech.04.09.html

STRAZZE93

I haven't done a tune up yet with spark plugs or anything and I have no idea how old they are. Im going to wait about a week and do a tune up and see how it turns out.
My idle is set at 800 but everytime i hit the gas it will idle down to a different number like 600 or 1000 it's weird.

4Crawler

iTrader: (3)

Dashpot sticking?
- http://www.4crawler.com/4x4/CheapTri....shtml#Dashpot