weird idle
10-06-2010, 09:30 AM
#1
Thread Starter
Join Date: Sep 2010
Location: Indiana
Posts: 4
weird idle
on my way to school i was coming to a stop light so i went into neutral to coast there. when my car went down to normal idle it then began climbing to around 1300 then dropped to normal and continued to do that until i came to a complete stop. any ideas what this could be?
10-06-2010, 10:38 AM
#2
Join Date: Sep 2008
Location: CO
Posts: 48
on my way to school i was coming to a stop light so i went into neutral to coast there. when my car went down to normal idle it then began climbing to around 1300 then dropped to normal and continued to do that until i came to a complete stop. any ideas what this could be?
10-06-2010, 03:50 PM
#4
2nd Gear Member
Join Date: Sep 2010
Location: Phoenix, AZ
Posts: 395
Sounds like it could be a vacuum leak. Check all the lines running to the IAC and just listen for air leaks. Pop your hood, and have someone else pulse the brakes slowly with the engine running, and you might hear the air leak, if there is one.
Last edited by Bmitchell373; 10-06-2010 at 06:17 PM.
10-06-2010, 06:06 PM
#6
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
The power brakes (not "breaks") on our cars do not vacuum assist, it is Ford's Hydro-boost braking system that uses hydraulic pressure from the power steering system.
-------------------------------
OP, what you describe are classic symptoms of a sticking IAC valve, here's how to test it.
The IAC can be tested by unplugging it while the engine is hot and idling--the idle speed should drop and the engine may even stall. If it does not then the IAC is likely sticking or sluggish.
The electrical resistance between the two terminals should be 6.0 to 13.0Ω, the resistance between either terminal and the IAC body should be > 10kΩ.
Last edited by cliffyk; 10-06-2010 at 06:12 PM.
10-06-2010, 06:20 PM
#8
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
I'm sorry, I didn't realise the OP had a '91 -- he'd be far better off asking his question in the proper section.
And they did use vacuum assist AFAIK, Ford had to use the Hydro-boost in the modular engined Mustangs because there was not enough room for a vacuum booster...
And they did use vacuum assist AFAIK, Ford had to use the Hydro-boost in the modular engined Mustangs because there was not enough room for a vacuum booster...
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