87toyy

My old man just bought a 95 4 runner 22re 5 speed, and when you apply the brakes it starts pulsing. The rpm's drop and raise steady until you let of the brakes and its runs fine. Anyone have any ideas what might cause this. None of the mechanics at the garage he bought it at had any idea what was causing it.

Elton

idle set to high

Junkers88

X2 what Elton said. Set the idle correctly and it'll stop.

bobby_duce

could a bad maf cause the same thing to happen?

MudHippy

No. But the 22RE doesn't have a MAF. It's got an AFM. Neither would have anything to do with what goes on with the braking system.

As far as the idle being set too high. I think something, or somebody rather, is too high. Because that's not going to affect the idle when the brakes are applied either.

Want to know what would cause that? Check vacuum the line running to the brake booster. It's leaking, or the booster itself is.

87toyy

Yeah i dont think it would be the idle. The previous owner bought a new brake booster for it, but it didnt help. I'll have to get dad to check the vacumn line. That was my first thought or a sensor.

lftd_86_yota

hate to start and argument... but it is indeed the idle. TURN IT DOWN!!

Junkers88

Someone is indeed high....

This has been covered several times. When you press the brake pedal the ECU reads that as a stopping situation and cuts the fuel, when the idle comes back up higher than normal then the ECU cuts the fuel again. Thus surging with the brake pedal pressed.

Teuf

Ding........ Round II.

MudHippy

Good call!
Me high? Highly intelligent maybe, but that's about it.

BTW, you're wrong. The brake pedal does not trigger fuel cut. EVER!

The ECM uses the IDL signal input from the throttle position sensor, the STP(stop light switch)signal, the A/C clutch status signal, and the ECT(engine coolant temperature)sensor signal to decide when to cut fuel WHILE DECELERATING when the engine rpms(Ne signal)are above the given threshold. The stop light switch signal(STP in these vehicles), triggered by pressing the brake pedal, the ECT sensor signal, and the A/C clutch status signal will increase or decrease that threshold WHILE DECELERATING. The ECM determines deceleration based on the VSS(Vehicle Speed Sensor)SPD signal input. If that sensor is telling the ECM that the vehicle speed is 0, as in the vehicle is stopped, then it uses the IDL signal ONLY to determine when to cut fuelling based on the current rpm threshold. The ECM disregards the STP signal because the vehicle is stopped. That input isn't needed to base the rpm fuel cut threshold on in that instance because it can't be used to determine deceleration or acceleration(there's no deceleration or acceleration when the vehicle isn't moving). The ECT sensor input and the A/C clutch status signal however, are still going to affect the fuel cut rpm threshold regardless of the vehicle's indicated speed. Which is why the FSM states to warm the engine to normal operating temperature, and have all accesories switched off, before checking the fuel cut rpm.

http://personal.utulsa.edu/~nathan-b...45fuelcutr.pdf

Full details on what I've presented are available on page 16 of the form below.
http://www.autoshop101.com/forms/h25.pdf

If you understand the intended purpose of the engine rpm fuel cut system, then it's plainly obvious why it only functions while accelerating/decelerating. It's supposed to increase fuel economy and improve emissions. Fuel economy is non-existent when the vehicle isn't moving, and emissions are as low as they get when the engine is at idle speed. So it's not needed under those conditions. Think about it.

Put simply, pressing the brake pedal while the vehicle is stopped/parked will do nothing to change the engine rpms. It doesn't matter how high they are. UNLESS there's a vacuum loss from the brake booster.

If this wasn't covered in the previous discussions/threads related to the issue being experienced by the OP, then it should have been. Sorry.

xxxtreme22r

I must be missing something here too, but doesn't that say:

meaning the vehicle is stopped ie 0 vss and the brake light has to be on only on the 2wd A/T?

87toyy

He was out with the 4 runner for a drive today, and the brake booster is new so we know thats not it. And the vacumn line seems to be all intact. No leaks that we could find.

muddpigg

iTrader: (1)

Mudhippy is a troll or idiot. On other post he was blaming pushrods for valve problems with a 22RE.

Turn the idle down as many others have posted.

MudHippy

I don't know why that would apply to 2WD A/T vehicles. I can only assume that for whatever reason, those conditions must be met to check the fuel cut rpm on those applications. But, keep in mind that's only going to lower the threshold rpm. As is clearly stated as one of the intended functions of the STP signal. See page 16 from the link below.
http://www.autoshop101.com/forms/h25.pdf

It will have no affect on the idle speed. The only way to affect idle speed is to vary the ammount of intake air past/through the throttle body, create a vacuum leak, change the A/F ratio by messing with the TCCS to supply more or less fuel, or change the ingition timing.. Plain and simple.
Dude, just stop. I haven't gone out of my way to insult you. If you can't stand being corrected when you're wrong then grow up or go home. Or just stop wasting our time by posting your uneducated guesses. You're obviously a piss poor mechanic with little to no experience or training. Whatever it is that you "think" you're contributing to this site is null and void because of that fact. So just quit making yourself look like an idiot. Please! Thanks!

BTW, has he even once mentioned that the idle is to high? Maybe because it isn't. To assume it is without checking it yourself, is naive. And doesn't help solve anything.

I make one misprint by substituting the word pushrod for rocker arm, and suddenly I'm a troll or an idiot? Come on! You're gonna have to do better than that. I've got 2633 post on this site, and such mistakes are EXTREMELY rare! Feel free to search through all those posts and point them out to me, if that'll make you feel better. Frickin' loser...

xxxtreme22r

One thing I don't agree with here is the posting of non-toyota guides to back this up.

In either case the FSM says the vehicle has to be stopped to test for the fuel cut and nowhere does it mention jumpering anything to simulate driving. Which tells me the fuel cut happens regardless of the vehicles speed. And if the vehicle is stopped it's in P not D which tells me it doesn't matter if your at a stop sign stopped or in your driveway idling with too high of an RPM.

That blurb about the brake lights being on on the 2wd auto and not the "others" is weird though too since we all know the fuel cut happens when the brakes are applied.

MudHippy

What? http://www.autoshop101.com/ is a Toyota specific, ASE certified technician training site. It has information that goes WAY beyond what's provided in any of the FSMs. And is extremely useful in understanding many Toyota specific electronic controlled and engine management systems. I'd have to say that I would have learned little about most of them without it's database for reference.

I'm just gonna leave this be as is. I've stated all the relevant information in regards to the OP's issue. At this point it's just another one of those "repeating myself over and over and getting nowhere" threads. Trust me on this though, it's not as complicated as it sounds.

Good luck!

xxxtreme22r

then explain how this fuel cut happens when vehicle is stopped during testing if the cut uses the VSS as a sensor for input.

muddpigg

iTrader: (1)

Yep post count means everything right. So your a kid studying for an ASE cert, cool. But don't get big headed.

So to recap the VSS tells the ECM to cut motor when the RPMs are 1300-1400 or over when brakes are applied. Why? safety: brakes + throttle = not good in most applications. We're not talking about drag racing.

Autoshop101 is a study guide with a large coverage of makes and models and years of the same make. Don't get it twisted. The FSM is specific to that generation Toyota. There are guys on here that know the FSM front and back.

To the OP, let us know what you find.

Junkers88

Simply put I had the same problem as the OP on an 89 4runner, 22re. Push the brake pedal (at a stop light) and the idle would surge. Turned the idle down from the 1200rpms it was running to the 850rpms it should be and the surging stopped. Didn't change any vac lines, fix any leaks, spray any parts or do anything else. This same problem has shown up several times on this forum and the fix is to turn the idle down.

You might be really really good at looking up things in a manual or posting some "findings" from Google auto shop but stay out from under a Toyota hood until you know what you're doing, no offense intended.

Junkers88

I agree 100% with that. Just turn down the idle (takes about 3 seconds and only one tool) and the problem will be gone.


OP let us know what you find.