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Old 01-09-2005, 11:10 PM   #1
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Default Idle adjustment

I have another one of my wacky ideas, that I have been contemplating. As you probably know, the ECU controls the IAC, which controls the idle RPM. Well, I remember reading, that the IAC - ECU communication is not duplex, and that the ECU sends the IAC signals, and that end it all. Well, is it possible for me to intercept that signal [or just cut the wires from the ECU completely], and have a little rotary switch, to lower or raise the idle RPM? I know the ECU would keep raising the IAC'* counts, even though no changes will occur, but will it throw an SES light? Will other performance factors be effected? The main reason I am doing this, is because I don't like the fact my idle is 1100RPM. I know it should be at 1kRPM, and it'* normal being in that range, I just don't like it, and I would like to have something lower, like 700 or 800 RPM instead. I would probably start seeing some negative effects below 700, so I probably wouldn't go below that.


-justin
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Old 01-10-2005, 12:34 AM   #2
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ur idea wont work sorry... it would be cool if it would though
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Old 01-10-2005, 01:02 AM   #3
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get an older car.
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Old 01-10-2005, 09:28 AM   #4
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idle is set from the factory you can alter it but its not reccomended there is a screw on the TB
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Old 01-10-2005, 12:12 PM   #5
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800 would be pretty cool and probably nice and quiet.
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Old 01-10-2005, 12:18 PM   #6
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i would take a moment to accept that the engineers who set idle as what it is set it that way for a reason.

and then i would leave it that way.

btw, what kind of idle does yours have on a cold start?
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Old 01-10-2005, 01:45 PM   #7
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Quote:
Originally Posted by jr's3800
Let me jump in and make a comment...

First have you verified the Idle RPM'* with a scantool?

Neither one of my cars looks like they are doing 750-800 Rpms by the tach, but when checked they are indeed idling as low as I would ever want an engine set...

As for the idle stop screw, you can adjust it but it will be a lost cause as the ECM will keep adjusting the idle down to 700ish rpms...

What looks like about 1000 Rpms on my 95 is actually more like 750 Rpms...


great point. our cars have *very* smart (read: adjusting to conditions) PCM'*... it'* going to do what it wants to do. it has more than one way to accomplish the tasks it has in mind.

and my idle is at about 750-800 rpm'* most of the time, once the engine is warm...
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Old 01-10-2005, 05:09 PM   #8
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How low can the idle go before these engines die?
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Old 01-10-2005, 05:13 PM   #9
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Hmm, that is strange. I know our gauges are so incredibly accurate . But, if the idle is off, wouldn't the higher RPM ranges be off too? Because, if the tach is 300 RPM higher than it should be, then I just revved the **** outta my engine. And no, I have not looked at anything with a scantool. My idle upon cold start, like cold morning start after not being run for a weak, is 1200 rpm. It drops 100 or 200 rpm after it warms up a little.

Mkaake: GM engineers don't impress me too much, so I don't think i'll leave what they did alone.

CmptrNerd: Yeah, it would be. My car kinda has a loud idle, not like exhaust noise, but just typical engine noise, and I just think that my idle is a little high.

I have two I/P'*, and both of them give the EXACT same reading. My guess, they are correct.

Anyone know what kind of signal the ECU sends the IAC? Is it voltage, or like what? Because, I really want to try it . Is it possible that I could adjust that screw on the TB so much, that the IAC couldn't raise any higher? Or is that never going to happen?


-justin
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Old 01-10-2005, 07:18 PM   #10
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Quote:
Originally Posted by opensourceguy
Hmm, that is strange. I know our gauges are so incredibly accurate . But, if the idle is off, wouldn't the higher RPM ranges be off too? Because, if the tach is 300 RPM higher than it should be, then I just revved the ***^ outta my engine.

Mkaake: GM engineers don't impress me too much, so I don't think i'll leave what they did alone.

-justin
1. if your tach is showing 300 rpm too high, than if you showed yourself revving the crap out of it, you were revving even more of the crap out of it. not the other way around.

2. should I point out that I am a GM engineer?

get a scan tool and find out what'* really going on. cars are mechanical systems. if something is wrong with it, there'* a reason. and fixing the reason is better than trying to artificially lower your idle speed.
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