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Trouble with engine idle

For all things Electrical.

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Posts: 223
Joined: Sat Sep 27, 2003 5:10 pm
Location: NW Sydney, NSW

Trouble with engine idle

Post by Impulsive »

Hi all,

I have a 1994 Sierra. I know that they have a small alternator, but I was wondering what could be causing my idle to go from the normal 750, up to about 1200 - 1300 when I switch on the blower fan inside the car.

It doesn't matter what speed it's on at. It just has to be on.

The car is fitted with air conditioning, but I don't have to have the air on for this to happen.

Any opinions are appreciated.
1998 Vitara Hard Top 2.0 EFI
65mm springs (by Allsprings)
35mm body lift
Rancho RS9000's
235's on 15in alloys
Flipped strut mounts
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Posts: 943
Joined: Sun Aug 24, 2003 2:42 pm
Location: Launceston

Post by Bluey »

i know some cars increase idle when air con turned on, possible that this is the case in sierra when fan on??? ie to compensate for small battery (or maybe heaps of other accessories eg family car) then turning air con/fan? automatically ups idle speed therefore delivering higher voltage to keep everything going.
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Posts: 223
Joined: Sat Sep 27, 2003 5:10 pm
Location: NW Sydney, NSW

Electrical Issues

Post by Impulsive »

Yeah, I guess it could be. The small battery theory makes sense.

I'll check a couple of other sierras to see if they do the same. Thanks for your reply.
1998 Vitara Hard Top 2.0 EFI
65mm springs (by Allsprings)
35mm body lift
Rancho RS9000's
235's on 15in alloys
Flipped strut mounts
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Posts: 4760
Joined: Mon Dec 30, 2002 6:04 am
Location: Adelaide

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Post by murcod »

Ferozas have a solenoid that opens to increase the idle when the fan is on (but they are EFI too....) Perhaps there's a similar thing with your Sierra's carby set up????
David
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Joined: Tue Jan 13, 2004 12:09 pm

Re: Trouble with engine idle

Post by mkpatrol »

Impulsive wrote:Hi all,

I have a 1994 Sierra. I know that they have a small alternator, but I was wondering what could be causing my idle to go from the normal 750, up to about 1200 - 1300 when I switch on the blower fan inside the car.

It doesn't matter what speed it's on at. It just has to be on.

The car is fitted with air conditioning, but I don't have to have the air on for this to happen.

Any opinions are appreciated.


Your A/C can be switched on & off with the A/C switch as well as the fan switch. Your A/C will actually swicht on & off with the fan switch to protect the system from overheating. I would say the main A/C (the one with A/C written on it) may be faulty & when you turn the fan on the A/C automatically comes on causing your idle up solenoid to operate.

The other way this can happen is the relay which operates the idle up solenoid is recieving a false reading from the fan switch when it is switched on.

See an auto electritian, they will be able to help
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