Question about 1994 Toyota Pickup

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Idle speed When I apply pressure to my brakes will running the a/c the engine begins to idle up and down

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Check your anti freeze'rs levels.. i had the same problem

Posted on Jul 13, 2008

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This is because the computer compensates idle for when the A/C compressor is on or off. When the A/C compressor kicks in the computer will increase the engine idle to compensate for the drag in from the compressor. When the A/C is off it will decrease the idle to try and maintain a steady idle. If it is causing a high surge when the brakes are on it may be the IAC valve. If it is just slight it shouldnt be anything to worry about.

- Tech101

Posted on Jun 23, 2008

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2.7 s type brakes not working as they should they are ok when you start breaking but when you are down to about 10mph the pedal becomes very hard to push and the car trys to roll on ?


It is possible the problem is ABS related but could equally be a problem with the vacuum servo or brake booster or the "supply" of vacuum.

Certainly best practice would be to begin by ensuring the brakes at each wheel are in good order.

Test the brake servo by pressing the brake pedal vigorously several times while stationary with the engine off. The pedal should then feel higher than usual and rock-hard.
Apply the footbrake with a moderate force and start the engine without using the accelerator pedal, if possible. The brake pedal should be felt to pull itself down under your foot immediately the engine starts and stop pulling down in just two or three seconds, maybe just a second or two more if it is a diesel model.

Release the brake, allow the engine to idle for a few seconds longer and switch off. Listen carefully in the resulting silence for the sound of air leaking. This might have to be repeated several times in order to listen under the dash and in the engine compartment around the brake booster and vacuum lines. A short piece of garden hose used as a listening tube can be useful.

Once a servo has been charged with vacuum, in the absence of leaks, it should remain charged for a long time if the brake is not used - certainly hours but often months or even years is not unusual. Aplly a moderate pressure to the brake pedal and a shhhhh... sound should be heard that lasts about a second and then stops. Increase the pedal pressure and another shhhh sound and stop.

If all tests ok you can be reasonably confident the brake booster and vacuum lines are in order though it is still possible the vacuum supply is insufficient for sustained braking. A road test on a clear and safe downhill route will determine if this is so. Make a rapid series of brief brake applications at a constant speed of around 30mph and the braking effort and the feel of the pedal should remain consistent and if it does not it indicates restricted supply pipes or hoses, poor engine tune, incorrect idle speed (petrol models) or a worn or inefficient vacuum pump if it is a diesel.

Jul 23, 2016 | 2006 Jaguar S-Type 2.7

1 Answer

I have a 90 chev blazer that runs rough when i apply the brake ,it also has a high idle and runs rich .?


I would look at the vacuum booster control unit .
This is the power assiest for the brakes it runs off the main engine vacuum,
If its leaking inturnailly you would lose engine vacuum that would make it run rough when you hit the brakes .
Also if the check valve inside of this unit were stuck it could cause a vary high idle
Try hitting the brake pedel when its idleing high in park and see what effict it has on the engine speed .
If it changes this is for sure your problem.

Mar 21, 2015 | Chevrolet Blazer Cars & Trucks

1 Answer

1990 Isuzu pickup turns off at stop sign


If this is a petrol engine have a look at the brake booster leaking vacuum and running the engine too lean to idle. Test by allowing to idle with out your foot on the brake If applying brake pressure shuts the engine down ,replace the brake booster..

Jan 24, 2015 | 1990 Isuzu Pickup

1 Answer

Stalling troubleshooting


run fault codes to check for electronic problems (TCM). If this problem only happens when the foot brakes are applied check for brake booster vacuum problem. Remove vacuum line and blank off and apply the brakes to see if the engine stalls at idle.

Jul 22, 2014 | Ford F-150 Cars & Trucks

1 Answer

Is it modulator valve, or other?


The vac modulator only assists the transmission in knowing when to shift up.
If the engine oil pressure gauge is acting wildly, it could be the sensor or the oil pressure could really be going up and down.

Feb 23, 2014 | 1994 Ford Aerostar Extended

1 Answer

2000 mercury villager, runs a fast idle. whether cold or warm the idle remains at a high idle speed, it even pulls with the brake applied.


Could be a vac leak, or a dirty throttle body, or a faulty idle air control valve. The computer controls idle speed by regulating the amount of air into the intake. Could also be something pulling on the throttle cable such as the cruise control.

Sep 28, 2012 | 2000 Mercury Villager

1 Answer

When slowing down to such speeds as 25 mph or lower the idle will act like it's starting to stall, then the idle will increase when i apply pressure to the gas pedal. during the time when the idle seems...


you must have a OBS2 scan and get the code for further help.
it can be a number of things.
go to autozone and see if they will scan it for you
as of the oil light when your engine Begin's to stall it will cause it to come on.
post some more info when you get the scan

Jan 19, 2011 | 2003 Ford Taurus

1 Answer

94 jetta 2.0 manual tran. engine stopped running at highway speed///have checked computer //fuel pressure regulator//engine management relay/// have fire on the plugs///have fuel pressure in the...


Sounds like the fuel filter. It would indicate the correct pressure at idle or maybe even revving. Once the engine is put under a load (highway speeds) it begins to choke. Try replacing the fuel filter.

Jun 29, 2010 | 1994 Volkswagen Jetta

1 Answer

Engine stalls when applying brakes. To prevent


You may have a dirty idle speed control valve, do the procedure below to correct this.

Get a can of intake cleaner (ABOUT $5.00) from any local auto parts store like NAPA or Carquest, do not use carburetor spray, intake cleaner only or u will damage the Teflon coating inside the throttle valve and air bypass valve, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

May 19, 2010 | 1995 GMC Jimmy

1 Answer

My 1998 900S run fantastic until you come to a red light. While applying the brakes the engine seems to shudder (idle up and down). Now I have an automatic transmission so the idle should be constant...


try the following it usually cure s this kind of problem
Here is the most common cause of surges and stalls at stops and low erratic idle speed and rough idle, it is the idle speed control air-bypass valve and throttle valve (IAC for short), they get full of gunk over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake

Mar 06, 2009 | Saab 900 Cars & Trucks

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