1990 GMC Truck idac (idle air control valve )

MAJOR2700

MEMBER
1990 GMC TRUCK
4 CYL
2WD
AUTOMATIC
101,160 MILES

I have a postal llv vechile can the idle air control valve cause a vechile to excellerate after taking out of park to a high rate of engine speed and show no code and braking still keep a high rate of excelleration with the brake on and only stop excelleration when you turn engine key off but when restarting engine seems to idle fine day temp roughly 70-80 degrees would it make sense to change the idac valve for safety

5 Replies

RASMATAZ

MECHANIC
75,992 POSTS

Clean out the IACV could be stuck in the extended position and also check the TPS

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Thursday, April 30th, 2009 AT 5:03 PM

MAJOR2700

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3 POSTS

I 'm told how to search to see if this is the problem but want I wanted to know can this cause a vechile to a excelerate out of control and only be stopped by turning off the engine

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Thursday, April 30th, 2009 AT 10:08 PM

RASMATAZ

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75,992 POSTS

Do you have a Carb or an EFI?

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Friday, May 1st, 2009 AT 10:54 AM

MAJOR2700

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3 POSTS

This vechile has a efi all I wanted was a answer yes or no if with what iI tolld you if this could be the cause of my problem, thank you for your help Roland

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Monday, May 4th, 2009 AT 5:32 AM

RASMATAZ

MECHANIC
75,992 POSTS

There's a reason why I've asked the type of fuel system due to different confirguration. Yes the IACV could caused that problem and other stuffs.

Too fast an idle speed. If an engine without computerized idle speed control is idling too fast and refuses to come down to a normal idle speed despite your best efforts to back off the carburetor idle speed screw or air bypass adjustment screw (fuel injection), air is getting past the throttle somewhere. Common leak paths include the carburetor and throttle body gaskets, carburetor insulator spacers, intake manifold gaskets, and of course, any of the engine's vacuum fittings, hoses and accessories. It is even possible that leaky O-rings around the fuel injectors are allowing air to leak past the seals. Another overlooked item can be a worn throttle shaft and a defective idle speed speed control motor/valve stuck in the extended (high idle speed) position/throttle position sensor. Also the throttle plate could be binding in its bore and kinked accelerator cable, coolant temperature sensor might not be operating properly misleading the computer that the engine is still cold and computer throwing fuel at it raising the idle speed.