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Old 10-14-2008, 09:11 PM   #1 (permalink)
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Altered Idle Speed After Performing EOC

I drive a 2003 Pontiac Vibe. I employ Engine Off Coast(EOC)ing regularly during my commute. I've noticed that, more often than not, my idle speed is up around 1200 RPM after bump starting at the end of the glide. Once I purposely let it idle for awhile (seemed like an eternity!) and it did finally 'relearn' and idled down.
So today I tried something. I keyed off a SECOND time (for about 2-3 seconds) during the glide. Bump start like normal at the end of the glide and...

Viola, idle's fine.

Then I just keyed off a little longer the first time, and it accomplishes the same thing. Nice low idle after the EOC. Apparently turning the key back to 'run' too soon affects the idle for some reason.

Anyone else experience this?

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Old 10-14-2008, 10:57 PM   #2 (permalink)
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The 1st Gen Vibe/Matrix employed a rev-limiter on warmup. I know this might be counter-FE-intuitive, but try this...

At the high idle, try an attempt at acceleration toward redline. If it holds at lower RPM (3000-4000RPM or so), then you know it has been fooled into thinking that you're still warming up.

It's one of the few vehicles I've driven actually prevents high RPM operation when cold.

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Old 10-15-2008, 10:31 PM   #3 (permalink)
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This morning I nailed the throttle as soon as I pulled out of the subdivision. It was in closed loop, but definitely not warmed up. It jumped to over 5k RPM. On the way home I got it to idle high after an EOC again and I punched it again. Again it raced to nearly 6 grand. So I don't think it has any kind of rev limiting.

As an aside, this thing goes into closed loop in less than five seconds after start up!
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Old 10-16-2008, 04:01 AM   #4 (permalink)
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my old es300 and camry do that wot throttle while the car is cold would give u about 3500ish rpm shift, and no od till it gets warm.


but my truck does that sometimes without oec, a slight tap of the throttle and it drops back to normal i always asumed dirty throttle body. maybe there is something to this.
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Old 10-16-2008, 08:52 AM   #5 (permalink)
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My truck has recently started doing the high-idle after EOC. I haven't tried varying the key-off time to see if it has an effect, but I have to generally keep the key off for 2-3 seconds to keep the engine from restarting on its own.

I have noticed that my factory original battery (in a truck manufactured Feb 2002, purchased Aug 2002!) is holding less of a charge. I plan to replace it this winter or it will surely die when it gets really cold. When I am in EOC I notice my voltage gauge dipping halfway between nominal and the "low" tick mark. I can no longer EOC at night or my headlights dim far too much far too quickly.

A lot of vehicles have an automatic high idle to bring alternator speed up and improve battery state of charge. If your ECU monitors battery voltage it could be trying to recharge after the bump start. Why this would be changed with a second key-off cycle I don't know, but it is another possibility.
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Old 10-16-2008, 09:37 AM   #6 (permalink)
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Yeah, the Matrix does this too. I don't engine off coast too much in it, but when I do and bump start it fluxuates a bit and goes to about 1200 rpm. Usually by then I'm already accelerating again so its no big deal.
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Old 10-16-2008, 02:05 PM   #7 (permalink)
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Quote:
Originally Posted by taco View Post
my old es300 and camry do that wot throttle while the car is cold would give u about 3500ish rpm shift, and no od till it gets warm.
The 'Teg does the same thing, even if it's 100F outside, or had been on the EBH (but not as much). 1200RPM, I believe, is the high idle setting. The trigger is a wax sensor that deforms under normal coolant temps to divert intake air.

What does stay the same the refusal to shift to 3rd until 2500RPM (I can force 2nd). This is a pain, since I need to motor along side streets for a about a mile until the 45 zone. I usually give it a quick boost up to 2600, let off the gas, and ker-plunk: 3rd. Light throttle at that point yields the best FE vs. racing along at 2100. The TC has a mind of it's own, though

Back to topic, I'm leaning towards the suggestion of voltage regulation for the spike in RPM. My batt is almost done as well, but I don't think it has this feature. When warm, the only time I get high idle is if I flubbed a startup and didn't crank long enough. Then, that second time around seems to take a while to fire up again and it high-idles for about 10 seconds.

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Old 10-22-2008, 02:02 PM   #8 (permalink)
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Well, shoot.
Keying off longer and doing a secondary key-off during a glide doesn't always work. In fact, not at all for a couple days. Then today it did idle back down after bump starting.
I've done several engine-on coasts up to a stop light. It idles high all the way to the light and then goes down after sitting at the light for about seven seconds. After ten seconds, it's idling around 700 like it ought to. Some crazy VSS logic?
I've heard of automatics holding a higher idle when coasting in neutral (a Saturn, IIRC), but Olivia's a manual.
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Old 10-22-2008, 02:23 PM   #9 (permalink)
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Yep, I've noticed this too with the Matrix. Its like it stands at the ready for a few seconds, then mellows down to 700 rpm if it thinks your not gonna move for a little while. Must be a performance thing is all I can think of. When I engine on coast, the rpms usually hover around 1000.
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Old 10-22-2008, 03:06 PM   #10 (permalink)
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OK, thanks Daox. Good to know it's nothing 'ABby Normal'. (Young Frankenstein reference)

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