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Jerry, Master Mechanic
Category: Buick
Satisfied Customers: 16835
Experience:  ASE Master tech. 30+ years mechanic, shop forman, service manager
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Car stalls when coming to stop

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car stalls when coming to stop

Hello and welcome to Just, Super mechanic here. About your vehicle.


Does it stall when you come to a stop when it is cold?


Does it start right back up in park?


Does it stall again when put into drive?

Customer: replied 6 years ago.

it stalls as i'm coming to a stop(5-10 mph) and also when stopped. it seems worse when the car is cold but it also does it when the car has reached normal operating temp.


The car will restart in N, and sometimes after starting(as when at a red light) I have to keep the car in N and apply gas to keep it from stalling.


it always restarts


Recently the car has become very hard to start first thing in the morning, and I have to apply slight throttle for about a minute to keep the car from stalling.


it sometimes surges as if it's going to die


There may be a problem with the idle air control circuit but you will want to make sure that the throttle body and idle air passages are clean.


You may want to do a throttle body cleaning on it. You can pick up some throttle body cleaner in most any part stores. You can follow the directions on the can but you will want to make sure that you give it a few shots with the throttle plate closed, so that the cleaner can get into the idle air passages.





Of course, you will want to make sure there are no vacuum leaks and that there is not any un-metered air that is entering into the intake, and that the air intake hose is on good and free of any cracks.

Customer: replied 6 years ago.
about a month ago when this became a problem, the mechanic cleaned the throttle body and intake. on my car specifically, what vacuum hoses should I check?

Any vacuum leak is a bad one....I have seen a few with some real soft vacuum hoses that go to the MAP sensor. They tend to colapse sometimes. But it is a good idea to check them all.


There could also be a problem with the idle air control valve. That would have to be checked with a tech1 type of scan tool.





Customer: replied 6 years ago.
how do I check for a vacuum leak, and on the quad four engine, where are the majority of the vacuum lines located? is the idle air control valve something that I can easily replace? I've worked on cars somewhat, but don't want to have to take apart the engine.

The vacuum lines will all go into the intake manifold. Mostly at the throttle body. If it is sort of intermitent, then it may just be the IAC valve. Pretty easy to change, (2 scerws)

















  1. Disconnect electrical connector.
  2. Remove IAC valve attaching screws.
  3. Remove IAC valve assembly.

NOTICE: If IAC valve has been in service, do not push or pull on the old IAC valve pintle. The force required to move the pintle may damage the threads on the worm drive. Also, do not soak IAC valve in any liquid cleaner or solvent as damage may result.


Clean IAC valve O-ring sealing surface, pintle valve seat, and air passage.

- Use carburetor cleaner and a parts cleaning brush to remove carbon deposits. Follow instructions on container. Do not use a cleaner that contains methyl ethyl ketone, an extremely strong solvent, and not necessary for this type of deposit.
- Shiny spots on the pintle or seat are normal and do not indicate misalignment or a bent pintle shaft.
- If air passage has heavy deposits, remove throttle body for complete cleaning.


If installing a new IAC valve, be sure to replace with an identical part. IAC valve pintle shape and diameter are designed for the specific application.

If installing a new IAC valve, measure distance between tip of IAC valve pintle and mounting flange. If greater than 28 mm, use finger pressure to slowly retract the pintle. The force required to retract the pintle of a new valve will not cause damage to the valve.

  1. Lubricate IAC valve O-ring with clean engine oil.
  2. Install IAC valve assembly.
  3. Install attaching screws. Tighten to 27
  4. Connect electrical connector.
  5. Reset IAC valve pintle position:
    1. Turn ignition switch to the "ON" position (engine "OFF").
    2. Ground the diagnostic test terminal for five seconds.
    3. Remove ground.
    4. Turn ignition "OFF" for ten seconds.
    5. Start engine and check for proper idle operation.
Customer: replied 6 years ago.

does it matter that the car starts in Nuetral?

No, that is what they do normally.



The IAC valve controls the amount of air bypassed around the throttle plate. This is actually a controlled vacuum leak. If more air is bypassed, idle speed will increase, and if less air is bypassed, the idle speed will decrease. The IAC valve accomplishes this by moving a conical shaped pintle in to decrease bypassed air and out to increase bypassed air. This can be seen as counts as displayed on a "Scan" tool. Inward Movement of the pintle = Decreased RPM = Lower Counts. Outward Movement of the pintle = Increased RPM = Higher Counts. The ECM uses sensor and switch inputs to control the position of the IAC pintle. If the pintle is stuck open, the idle speed will remain high. If the pintle is stuck closed, the idle speed will be too low, and stalling may occur. If the pintle is stuck partially open, the idle speed will be higher than normal, and there will be no response to changes in engine load such as A/C ("ON") or transmission in ("Drive").

Customer: replied 6 years ago.

My car never idles high, only low. Does this rule out a vacuum leak, as vacuum leaks cause a high idle? Should the IAC valve be the first thing I should replace/rule out?

Yes, the IAC valve should not allow the engine idle to go so low that it stalls.
Customer: replied 6 years ago.
is there a particular brand that i should purchase?
Normally the after market ones are less expensive. You might even want to try a used one from a salvage yard when not sure, to see if it will help.
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