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Old 01-17-2009, 08:10 PM   #1
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lowering your idle

I thought I read this somewhere, but I miss read it. but it's an idea. your probably saying it's not going to do very much, but every little bit helps though right. like not using your lights or radio, running stop signs, etc. if say your idle is 750 +/-. what about droping it down to say 650?? what do you think?
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Old 01-17-2009, 09:03 PM   #2
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Quote:
Originally Posted by guest001 View Post
I thought I read this somewhere, but I miss read it. but it's an idea. your probably saying it's not going to do very much, but every little bit helps though right. like not using your lights or radio, running stop signs, etc. if say your idle is 750 +/-. what about droping it down to say 650?? what do you think?
Lowering your idle if you can would definitely save fuel, the problem is it's generally difficult for one to lower it without it causing the engine to be unstable, misfire etc. If you were to adjust your cams either by replacing them or adjusting their timing, it's possible that you'd be able to lower your idle and have it be stable. Cam timings are the primary reason why race cars have such high idles such as 1000 or 1500rpm, it's because not enough air gets into the engine at the slower speed and therefore causes it to basically not run. If you want to lower your idle, go ahead, just be prepared to see it not run properly due to stock ECU settings and not having an appropriate cam.
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Old 01-17-2009, 09:28 PM   #3
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I'm sure lowering your idle is much like overclocking PC's and such: The manufacturer has it set a lil bit higher than necesarry, and some cars may tolerate it running lower than others. For best results, tweak it a bit and see how low it'll go and be stable under your operating conditions.

Good luck!
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Old 01-18-2009, 06:59 AM   #4
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Most cars control idle speed via the IAC which is controlled by the computer, so reprogramming would be necessary.

If you have a manual transmission, the lower idle speed may lead to an occasional stall, in which case any fuel savings from the lower idle would go out the window (unless you idle for hours and hours). Even on an automatic, you might stall occasionally during deceleration, although usually the computer can "catch" the engine on its way down.

On a carb'd car, this could be a good idea, but not many of those around any more...

-BC
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Old 01-18-2009, 01:17 PM   #5
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I think you're inviting possible cam and rocker arm wear.

Use a decent oil, preferably one with plenty of high pressure additives (zinc, moly, etc.) and consider having an oil analysis performed. You might ask around at http://www.bobistheoilguy.com/ and read the faqs too.
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Old 01-18-2009, 01:48 PM   #6
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It might not save fuel, don't forget that.
Lowered piston speeds will reduce turbulence and distribution of the injected fuel. It might require more fuel to be injected due to compensate for less than optimal combustion. Idle speed mixtures already tend to be slightly more rich than mid range engine speeds. Lowering the idle speed further than intended could make any increase in fuel to air mixture use more fuel than fewer strokes per minute might.
Lowered idle speeds will quite likely require richening the idle jets on carbureted engines due to a much lower venturi effect and reduced vacuum. This also will quite likely result in more fuel use than a lower rpm saves.
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Old 01-19-2009, 05:49 AM   #7
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Also don't forget that smaller motors might be needing to make a certain amount of power at idle to keep accessories turning. On a bigger motor, the minimum fuel that will keep the motor and accessories turning might not be much different from what the minimum is to fire the motor, but a smaller motor, might need a certain amount of fuel for that.
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Old 01-19-2009, 05:07 PM   #8
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if u have a carb its easy lol got the chevette down to 200rpm.

has idled at 100 before, was a tad odd...

it doesn't misfire one bit or shake anymore than it did before at its ridiculous 900 rpm stock idle.

yes at night if i have the lights on they will dim at its 200 rpm idle, if i slowly increase it to 3-400 they become normal brightness. but really im driving more than idliling (living in the boonies with the occasional stoplight/stop sign) so i dont have to worry about the battery dying thats already way to big for the car.(took it out of my sisters 96 saturn when it blew up, fit in the chevette and been using ever since)

i believe it helped fuel consumption a little bit cuz now its cold fast idle is about 900-1000 instead of 1300. that and installing a manual choke helped alot.

i can shine a light down the carb with it runnign and see no fuel whatsoever comin from the fiel lines in it. if i snap the throttle i can see it spray a shot down it lol
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Old 01-19-2009, 05:35 PM   #9
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100rpm on a 4 cylinder...I bet you could hear each power stroke.

If I yank the throttle on my Buick's carb, I can see fuel come out like a squirt gun.
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Old 01-19-2009, 09:06 PM   #10
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hahah you can. i snagged a pic when i was running seafoam thru it while it was idiling slow. also took a vid but gotta upload it to photobucket



whats a fun thing to know the ford model A engines idle is 60 rpm
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