1990 GT A/C Idle Problem

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azjeweler@gmail.com - 07 Sep 2006 04:46 GMT

I have a 1990 GT and when I turn on the A/C it makes the car idle much
lower than it should be...i have been told that this is some sort of
part that is supposed to increase the idle when the a/c is switched on
but i haven't been able to confirm where it is; the car will even idle
out nad turn off if I leave the a/c on in park for a couple of
minutes...any ideas guys????

thanks

GT5OH

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lugnut - 07 Sep 2006 14:42 GMT

>I have a 1990 GT and when I turn on the A/C it makes the car idle much
>lower than it should be...i have been told that this is some sort of
[quoted text clipped - 6 lines]
>
>GT5OH

You have a dirty/gummed up IAC. There is a chance it can be
cleaned but, many require replacement. Easy to replace.
Cost around $50-$80 for part. I suspect your engine idle
does not correct at other times either - like when you place
it into gear unless it is a manual in which case you may not
notice. You have probably also lost your cold high idle on
startup.

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sleepdog@optonline.net - 07 Sep 2006 14:57 GMT

> I have a 1990 GT and when I turn on the A/C it makes the car idle much
> lower than it should be...i have been told that this is some sort of
[quoted text clipped - 6 lines]
>
> GT5OH

Could be IAC like the other poster mentioned, but what exactly are the
idle speeds in question? Check your tachometer and post your findings.

- Initial startup, should be under 1200 rpms
- After a few minutes after startup, should decrease to about 950 rpms
once it is warm
- Get the motor good and warm, turn the AC on, should drop and readjust
to about 950.

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sleepdog@optonline.net - 07 Sep 2006 14:59 GMT

> I have a 1990 GT and when I turn on the A/C it makes the car idle much
> lower than it should be...i have been told that this is some sort of
[quoted text clipped - 6 lines]
>
> GT5OH

Shoot I saw 1990 GT and I automatically assumed an Escort (like I
have...). You're obviously referring to a Mustang GT 5 Liter. Sorry!
Disregard my other post because I don't know the idle speed for your
car.

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Backyard Mechanic - 07 Sep 2006 23:49 GMT

>> I have a 1990 GT and when I turn on the A/C it makes the car idle much
>> lower than it should be...i have been told that this is some sort of
[quoted text clipped - 11 lines]
> Disregard my other post because I don't know the idle speed for your
> car.

Idle speed is about 600-650 on v8. Should be 500-550 with IAC harness
off.

IAC idle warm about 750 on v6 and about 900 on 4 cyl

Replace IAC, dont bother cleaning it.. unless you have just a sometime
glitch and want to see if that affects it... cleaning often changes the
idle symptoms, but also often never works right all the time.

Signature

Yeh, I'm a Krusty old Geezer, putting up with my 'smartass' is the price
you pay..DEAL with it!

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ShoeSalesman - 08 Sep 2006 07:48 GMT

>>> I have a 1990 GT and when I turn on the A/C it makes the car idle much
>>> lower than it should be...i have been told that this is some sort of
[quoted text clipped - 19 lines]
> glitch and want to see if that affects it... cleaning often changes the
> idle symptoms, but also often never works right all the time.

and clean the throttle bore while your at it.

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