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My wifes 2000 Forester, manual transmission with 175k miles run fine unless the blower motor is on. The idle jumps up to 3000 to 400o rpm and will drop to normal when switching blower off.

As winter approaches running without a heater/defroster is hardly an option.

Any ideas?

rick

w mi.

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You may want to have the alternator or battery checked. I know when the voltage is low the ECU will raise the rpm to increase voltage and charging.

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There have been odder things....

 

 

Good place to start, though the jump sounds awfully high as alt output hits max above 1800 rpm.

 

What happens when the defroster is on?

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Do the headlights dim when you turn on the blower motor?

 

Automotive CPUs are desigend to be very resistant to interference from EMF, but you might give this try. Turn your car radio to an unused spot on the AM band, the FM band will not do. Turn on your blower motor, do you LOTS of VERY loud static?

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Prolly worth a trip to an Autozone or Advance Auto Parts store, or similar place, and have them check out the charging system. They don't charge for this, and they will tell you if there is a problem with the alternator or battery.

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Battery voltage hangs around 13.8 to 14.2.

No am radio noise.

Haven't checked what effect the defroster has.

Maybe tomorrow.

How does that figure in the scheme of things?

 

rick

w/mi

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Could be a bad ground. Put a voltmeter from the intake manifold to the car body. What are the voltages with the blower running and without?

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Battery voltage hangs around 13.8 to 14.2.

No am radio noise.

Haven't checked what effect the defroster has.

Maybe tomorrow.

How does that figure in the scheme of things?

 

rick

w/mi

 

defroster mode kicks on the AC compressor. AC-compressor-on raises the idle.

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I would inspect the hoses from intake tube to IAC, and from IAC to the thottle body.

 

Idle Air Control valve. IIRC, it's located on the passenger side of the intake. About the size of a sharpie pen, with a couple tubes, and a purple connector.

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