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Low idle speed with A/C engaged
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hawk42
Novice
Jul 20, 2012, 10:15 PM
Post #1 of 2
(3384 views)
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Low idle speed with A/C engaged
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Make: Ford
Model: Probe SE
Year: 1995
Engine: 2.0L DOHC 4
Transmission: Manual 5-speed
When the A/C is turned on, the engine idle speed does not increase to compensate for the compressor load. The compressor engages and the cooling fan starts. However, there is no increase in idle speed resulting in an idle of about 450 RPM's and a laboring engine.
This Probe (Mazda engine/drivetrain/controls) utilizes a IAC valve mounted on the top of the throttlebody that is both thermostatic and electrical. Engine coolant flows through the valve. It also has an electical solenoid incorporated into the top of the valve utilizing a 2-wire connector.
Apparently the thermostatic portion works correctly as the idle speed is increased upon a cold start and drops to about 850 RPM's as the engine warms up to operating temperature..
I have checked the resistance of the electrical solenoid found on the IAC. According to my Chilton "Total Care" manual, the resistance should be between 7.7 and 9.3 ohms. This one checks 9.1 ohms. It has been sometime back since I checked it but then I was not getting any electrical signal to the solenoid when the A/C was operational. Here again, I am assuming the electrical solenoid is what increases the idle speed for A/C operation but that may not be the case. The wiring diagrams found in the Chilton leave alot to be desired as to this level of detail. If A/C operation is routed through the ECM, then portions of that must be operating properly as the compressor engages and the cooling fan starts.
This vehicle now belongs to my son but it has been in our family 12 years and I know the idle speed used to increase during A/C operation.
What I am hoping for is that some of the moderators/members may be familiar with the controls on this vehicle and the method utilized for increasing idle speed during A/C operation or perhaps access to a more detailed wiring diagram.
Any assitance with this problem would be appreciated. Thank you in advance.
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Hammer Time
Ultimate Carjunky
/ Moderator
Jul 21, 2012, 3:19 AM
Post #2 of 2
(3344 views)
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Re: Low idle speed with A/C engaged
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They all pretty much work the same. The IAC is the tool that has the ability to increase idle and the PCM is programmed to operate it.
You may have a bad IAC ( idle air control) but try eliminating any vacuum leaks and cleaning the throttle body first. Remove the intake snorkel, have someone hold the throttle wide open for you and scrub the back side of the throttle plate and surrounding bore with an old tooth brush and some carb cleaner. Be sure to spray some into the small holes next to the throttle plate. That should help stabilize the idle. If it still has a problem, replace the IAC.
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