The California Kid

So when the engine is nice and warm, like after driving it for 20+ minutes, my idle will bounce around.

I'll pull up to a stoplight with my foot on the brake, and the idle will drop down to about 600, then jump up to about 1,300 repeatedly until I take my foot off the brake. I looked for vacuum leaks around the engine, and used a whole can of carb cleaner trying to find something, but came up empty handed. Any ideas?

Myron

i would say you have a vacuum leak some where. There is a post i came across where some one said to spray some wd40 or something on the lines and you will know when you find that leak...DONT QUOTE ME..

Good luck..keep us posted since a few of us are having that issue.

GoFish

When you ask for help you need to provide some key nfo like year, engine, etc. There are some really knowledgeable people on this board but no psychics.

This sounds like your brake booster going bad. This is a fairly common problem for older trucks. You can grab a brake booster from a wrecking yard or u-pull for 20-30 bucks.

project91

If its a 22re..the black screw with the spring around it on the upper intake needs to be adjusted.

The California Kid

Sorry guys. It's an 88 4runner with a 22RE 5 speed.

And the WD40 trick is actually carb/throttle body cleaner that you spray around a suspected vacuum leak. The vacuum leak will suck the fumes from it and send it through the intake, and stumble because of the rich mixture.

Is there any way to test my brake booster?

abecedarian

sounds like the brake booster since it happens when you're on the brakes.
you'll need to spray whatever you're going to use on the INSIDE of the cab where the rod goes through the firewall.

MMA_Alex

+1 for the brake booster. The diaphragm will tear over time, and when it tears you get a vacuum leak by stepping on the brake pedal.

the other testing option is to hook up a vacuum gauge,and with the engine running see how the vacuum changes (or doesn't) while stepping on the brake pedal

The California Kid

BRILLIANT! I'll spray some more carb cleaner under my dash tonight and see if I get anything.

Matt16

Your idle speed is set wrong. When the brake is on, the fuel cuts off at 1300rpm or so.

abecedarian

Huh?

There is a 'high rpm fuel cut' but not a low cut.

Junkers88

I had this same problem and it turned out to be a leaking intake gasket. Just keep checking things and let us know.

abecedarian

you do realize that if that is true, and I'm at idle and step on the brake, my fuel would be cut causing my engine to die since my idle is about 800.

ScottyC

iTrader: (1)

Actually that is true. The 22RE has a provision that does in fact cut fuel off when the brake is applied over a certain RPM.

This is straight from the FAQ on Pirate:
"The EFI computer receives a signal from the brake circuit that tells it that the brakes are being applied. This causes the computer to shut off the injectors if the RPM's are over a certain level and the engine is in "closed loop" as engine power should not be needed if the brakes are being applied.I believe the set point for the injector cut out is 850 to 900 RPM. This is what causes the surging - your idle RPM is too high, when the brakes are applied the injectors are cut out until the RPM's drop below this level. The engine then run's again. This only happens when the engine goes into "closed loop" so this will not happen when the engine is at a higher idle speed warming up. I am willing to bet your idle speed is around 1000 RPM when this happens. To fix this problem, simply adjust your warm idle speed to 750 RPM as per the factory. "

Matt16

There is actually a low speed cut off. That was the cause to my loping idle when on the brake.

The ECU receives knows when the brake light is on. There is no sense in dumping burning extra fuel while braking. When you braking and and the engine speed is at 1300 or so RPM, the ECU cuts some of the fuel.

When the idle speed is set wrong and your brake is on, the engine idles up to the mark, then the fuel is cut, the idle speed drops, the engine allows more fuel in it idles up hits the 1300 mark, cuts out....

This is a fact. Pay attention while you're braking next time. As you brake with the engine in gear, you'll feel the truck all of a sudden slow faster when you drop past 1300 or so rpm.

abecedarian

From what I know, the ECU senses the throttle plate is closed via the TPS and its IDL circuit and if the engine RPM's are above ~1500, there is a fuel cut in order to reduce HC emissions. Once you drop below those RPM's fuel flow is restored to the pre-programmed idle mixture level, but the ignition timing also changes to its baseline which will cause an apparent increase in engine braking efficiency.
Whether you are are appying the brakes or not is irrelevant, but the affect is more apparent since the engine braking supplements, or adds to, the braking force you are applying with your foot.
You can feel the effect even if you are not in gear, if you're paying attention.

The California Kid

When I had it smogged, one of the reasons it failed was for high idle... i'll adjust the screw to 850 RPM???? Then go from there?

It idles now at 1000

abecedarian

warm idle on a 22re should be ~750. if you can't get it below that, the TPS, timing, coolant temp sensor and the IAV/AAV need checked.

abecedarian

EVERYTHING depends on the engine warmed up and the idle at 750 and the ignition timing at 5 BTDC (UNLESS the decal under the hood states otherwise)

It does NOT matter how the engine runs if the above settings are not correct. The engine MUST operate as mentioned above or nothing else is correct. Adjusting and correcting EVERY other condition in the engine is based on and around those two parameters.

Cold engine idle, A/C idle up, EVERYTHING depends on the above mentioned settings.

MMA_Alex

its an adjust screw on the throttle body. Its on the left side of the forward part of the tb, facing upwards (if i remember right)

yes the idle can not be properly adjusted if the timing isnt right, and the timing cant be properly adjusted if the tps isnt adjusted right

ps. there are 2 different idle speeds for manual vs. auto transmission.

most of this information as far as tuneup specs should be on a sticker on the underside of your hood

Matt16

You seem to have have a better sense of the mechanism than I do, so I'll dispense with the pedantics. All I know, is that:

1. my idle loped while the brake was on
2. i had no vacuum leaks
3. adusting the warm idle from 1000rpm (idiot PO) down to 750 fixed the problem