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?

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.

RH77

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!

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.

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.

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.

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 :rolleyes:

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.

RH77

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. :confused:
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? :confused:
I've heard of automatics holding a higher idle when coasting in neutral (a Saturn, IIRC), but Olivia's a manual.

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.

OK, thanks Daox. Good to know it's nothing 'ABby Normal'. (Young Frankenstein reference) :D

maybe it is an emmisions thing?

I think most cars have a high idle on start up to help the car warm up quicker. I've seen most of my cars do this high idle right after start even if they were already warm.

well my truck did that before i started eocing. but a slight tap of gas always settled it. so i blamed it on a dirty throttle body

Some manual tranny setups do that to prevent stalling on take-off.

My father's 2001 S-10, 2.2 with a manual, acts as if the A/C is on when engine-on coasting in neutral. Idle sits 11-1,200, where sitting at a light is around 850-900.

My bike of course won't EOC at all above 15, due to it's centrifugal clutch. :rolleyes:

And something about GM vehicles, they foul the TB like a diesel engine. I've cleaned the TB on my truck shortly before I got rid of it, (at only 16.5k miles, no less), my mother's Blazer, my father's bravada, and his S-10. Only one that doesn't do it is the Eldorado. Clean, virgin TB's, intake, everything at 70k, and it gets 30mpg on the highway, no hypermiling at all. :eek: I swear this car is a fluke.

Now if only Cadillac could be convinced to downsize the Northstar for other purposes, like a .4L version for my bike. :rolleyes:

but his car is not gm....it just wears it clothes:)

and milage i have 252k :)

I know it's not the same GM from the old days... But I thought it was made along with all the other American makes... In Mexico. :confused:

Or did you mean the Cadillac? (My mother's)

http://www.nummi.com/
what we make

cali made while the matrix is made in canada no mexico here.

Doesn't have any of my parents fleet listed. :confused:

Edit: Oh but the Vibe! I see. Still, I'm not particularly fond of U.S. makes right now. Crap can be built anywhere. :D

the higher idle could be to boost alternator output or to get the steering fluid moving or fan going (again alternator output) or even to boost vacume to boost brake pressure.