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Join Date: Aug 1999
Location: Huntington Beach, CA, USA
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Question Idle and headlights

I've noticed that my idle loses a little rpm and gets rougher when I turn on my headlights. Is this normal? Idle is nice and smooth at 850 rpm when the lights are off. My car is a stock 1974 914 2.0 with FI. Thanks.
Old 11-15-2002, 08:44 AM
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Hello,

I have this exact same problem on my stock 75 1.8 L-Jet! and was wondering the exact same question just this morning. Why is this happening, and what can I do about it?

I did find this thread to be of some help except I have the L-Jet.

Electrical Problem

Thanks,
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1979 911sc
1973 914 2.0

Last edited by rockaria; 11-15-2002 at 09:07 AM..
Old 11-15-2002, 08:58 AM
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check the specific gravity of your battery first. add electrolyte or distilled water if needed. are you running stock wattage headlights? i had a loose red/alt wire at the battery which gave be similar problems. the voltage drop with the lights on could be messin with the fi.
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Old 11-15-2002, 09:28 AM
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Porsche Crest Alernator is working harder

As you can imagine, the lighting system sucks the most electricity.

When the car is just tooling down the road on a bright, sunny day it uses barely any juice at all, with the "extra" going to charge the battery. The voltage regulator prevents the alternator from overcharging the system.

As the alternator ages, it has to work a bit harder to produce that same voltage (brushes don't generate as efficiently I have been told.) Well, when you flick the lights on, a great deal of juice must be generated to operate the lights, run the car (spark and ECU) and continue to charge the battery. To generate the extra power, the alternator puts a greater drag on the belt, effectively sucking extra horsepower from the motor. Not noticeable at speed, but at idle it will drop the idle speed. If you turn on your lights at night and then turn your dash lights all the way off, you may see your generator light glowing faintly.

Modern cars have a ton of things that produce drag on the motor (power steering pumps, power brakes, alternator, vacuum pumps to operate other power goodies) and a great deal of research goes into reducing those peripheral power demands. Some cars have little electrical motors that drive those pumps instead of relying on belts, which pull the power directly from the crank. Dragsters don't even have alternators, they run directly off of the battery for their 10 second blast down the strip.

The question on what to do about it? If your voltage generated drops to under 13 (should be around 13.5 - 14 when running at speed) you may be on your way to having to replace the alternator. Sorry
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Old 11-15-2002, 09:40 AM
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My car is a 74 2.0 also. And I have the same problem.
Mark
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Old 11-16-2002, 06:41 AM
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Check out pbander's website...

http://members.rennlist.com/pbanders/

Click on the diary. Look for "Finally solved my idle problems". Actually the whole diary is worthy readiing.

THis is a common problem and has more to do with the proper tuning and setup of your engine than bad electrical connectors, bad batteries, bad alternators, etc.

Regards,
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Old 11-16-2002, 06:47 AM
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It seems to me that this may be a somewhat normal condition. Is there anyone out there who's car doesn't do this?
Old 11-16-2002, 10:47 AM
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