Intermittent high / fast idle? - Page 3

On Tue, 09 Aug 2011 11:18:28 +0100, Dave Plowman (News) wrote:

[...]


*I* wouldn't want to; if you'd read up-thread, you would see that's what
BMW do with the Mini...

Chris

--
Remove prejudice to reply.

I'd guess this is more to do with the engine start/stop system. Rather
than a general benefit.

--
*If you're not part of the solution, you're part of the precipitate *

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

On Wed, 10 Aug 2011 11:16:07 +0100, Dave Plowman (News) wrote:

[...]


Thinking about it, if you have to raise the idle when running in order to
keep the battery charged for all the restarts, you're not going to be
saving a great deal of fuel.

Chris

--
Remove prejudice to reply.

--
*Can fat people go skinny-dipping?

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

In fact this isn't that simple to do that accurately is it?. You'd need
to know where a lot of currents are going to make it anywhere near
sensible i.e. what's coming off the alternator what's going to or coming
from the battery what's going into the cars electrical system..

It would seem that all you need to do in effect is to voltage and
current limit the alternator output. That is perhaps all thats really
required.

Unless you might need to know what the alternator is "pulling" off the
crankshaft in order to regulate the engine load, but then again if your
doing that you'd need to know what the water pump is doing 'tho that
seems like a constant load .. the steering pump and brake servos etc
hardly seems worth the bother..

The load pulled by a aircon pump is a significant one so some means of
measuring what thats taking is perhaps in order, how you'd do that is
interesting perhaps if the Aircon is ON then you'd add in "x" amount of
fuel mix extra for an assumed constant load..
--
Tony Sayer


                

Not at all..


Snipped a tad..

Only thing that -seems- it has much to do with it is elevated
temperature. I've got an almost identical problem on the Audisaurus and
when it was hot the other day it was almost up to 2000 RPM on idle and
would not respond to the quick flick on and off of the ignition switch
which clams it down to 800 odd..

I too have a replacement pattern e-bay idle valve and I sometimes wonder
if that might be the cause..

I'm minded to clean out the original which was causing stalling and see
if thats any different..
--
Tony Sayer

It does seem temperature related - and seems to be when the engine has got
truly warm from running / driving a while, rather than just showing normal
coolant temperature.

Turning off, then on, doesn't seem to help mine.


After a while of using the new one, I did wonder whether there was anything
wrong with my original - at least anything other than needing a good clean.

I've not had any repeated instances of blipping the throttle driving the
high idle even higher - I sort of attributed that to issues with the IACV.

Further update - perhaps some progress...

I got a chance to plug in my newly acquired USB thingmy (ELM interface -
£13.95 from ebay, with some software - easyobd, I think it's called). Have
to say, it's been worth every penny.

So I took my laptop and interface out to the car, connected it all up
started the car. Idle was perhaps normal for cold, but didn't seem to drop,
in fact slowly rose and started to race at 3k and climbing.

I had the software connected, and could see quite a lot of parameters, and
inspect the output / readings of quite a few sensors. The coolant and air
temperature readings all seemed very plausible and valid (coolant temp
raising as you'd expect). Wasn't sure what to expect with some of the other
sensors (02 for example, and there was 2 readings - the first showed an
indication of running rich / lean - as did another reading on fuel trim).

There was readings for engine load (calculated), battery volts (presumably
however the ECU measures that) and "Absolute Throttle Position".

When it was playing up - ie revs climbing and racing - nothing looked
unusual, other than the revs - coolant temperature was rising as you'd
expect. "Battery volts" didn't show any particularl change (on all readings
and logs, seems to be somewhere between 13.9v and around 14.2v).

The one thing that struck me as slightly odd, from the very off (ie engine
start at truly cold - not been started for about 3 days) was that the
"Absolute Throttle Position" was ranging from somewhere above 7.0% to
9.something% - I wasn't sure what to make of that - either the variance, or
it being above 0%, given my foot was well away from the throttle pedal. When
the engine started to race, there wasn't any notable change in this value.

Blipping the throttle, at this point, just pushed the revs higher. So I
disconnected the IACV. Absolute Throttle Position value went to 0%, and then
there was a code pending - no active code, mind, nor any MIL.

Monitored it like that for a while, and it largely behaved like it had done
in other instances of disconnecting the IACV (ie just electrically by
removing the plug). Looking at other measurements, the engine ran richer at
this point (ie with the IACV unplugged).

After a bit, I wondered what would happen if I plugged it in again - would
the engine start to race, or would it just settle. So I did - idle dropped
to somewhere in the normal region (a little over 900). And stayed like that.
And Absolute Throttle Position remained at 0%. Engine behaved perfectly,
even in response to blipping the throttle.

Thinking that I'd only termporarily "tricked" the ECU into thinking
everything was OK, I saved the current log of readings. And turned of the
car. I started it again, switched on the software to watch all the
parameters (it would be pretty much well warm by this point), again idle in
normal(ish) range (a little over 900 - I perhaps would have expected around
the 850 mark, but 900 and a bit is considerably more normal than 1500 rising
to 2k and beyond), absolute throttle position still 0%, calculated engine
load perhaps lower than previously.

Not wanting this to be a fluke, I saved the current log of readings, then
turned off. Gave it a few seconds, then turned it on again, and started
monitoring - exactly the same - pretty normal idling (low 900s), absolute
throttle position still 0% and unchanging unless I moved the throttle pedal,
everything looking normal, no problems, no pending codes, everything looked
(as far as I could see) normal.

A few hours later, I drove the car for a fair while, some local movements,
then a reasonable run of around 30 minutes. Everything seemed to behave as
normal - no high idle, no issues at all that I could see. After being parked
up for a couple of hours, made a return journey of about 30 minutes - same
again, everything seemed normal and fine.

So concluding from that, I could only think that some learning of the idle
was needed by the ECU (after all, I'd reset it a few times by either
removing the ECU fuse, or by doing so with my code reader) which makes me
wonder, could it possibly be a required step to plug in the IACV (or a new
one) after letting the car idle a bit, and then idle trim is established?

That's how it looked from monitoring it, and it's behaviour for the rest of
the day. Any comments or feedback on that theory welcome - either way.

Problem is, that sounds a little strange to me, and I've had instances where
I thought it had all gone away / been fixed, only for it to return with a
vengance some days later.

Still, at least I have something of a trick that seems to keep it running
fine for a while, if it happens again.

Thanks for your patience, if you're still reading this!

You can't get an indication of anything other than the correct mixture
with the engine hot. That's all a narrow band lambda sensor can tell you.
And the mixture will be rich while the engine is warming up.

--
*Time is what keeps everything from happening at once.

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Well there was 2 different metrics - one of them was "Short Term Fuel Trim
Bank 1" which seemed to flip / flip between being lean and rich most of the
time - 'cept when the IACV was disconnected, then it seemed to show
consistently rich (the first O2 sensor seemed to largely be congruent with
this reading, too). When it was plugged back in again, it went back to being
largely lean, with the occasional flip / flop to rich.

I don't know how accurate the gizmo and / or software is, but it was just a
curious thing, really, unplugging the IACV definitely seemed to have a
bearing on it running rich. That said, other than being something to note of
interest, I don't think that particular finding adds much to either the
problem diagnosis, or resolution of it - but as it related to the IACV being
(electically and physically) present, I wasn't sure if it had any bearing.

Its quite possible that you might have a duff joint somewhere around
that un plugging and re plugging the IACV lead may well be disturbing
which will be OK for a day or two or three or more. Such is the way of
modern electric's..

I have read about this ECU learning but it seems that the ECU might be
learning the wrong things..

Anyways I expect that a garage doing the same job might be finding this
just as awkward to fix except that its often very useful to have spares
around to swap out just in case you might have a duff new one, and I've
seen that in other applications more than the once;!...

Keep us all informed of progress!...
--
Tony Sayer

                

Only thing to report as an update, is the problem still occurs. But whilst
it's happening (ie engine fully warm, revs racing at, say, 2k, when it
should be idling), disconnecting the IACV (electrically, by means of the
multi-plug) and reconnecting it cures the problem for, at a rough guess, a
couple of days. I've since done this procedure about 2 or 3 times, recently,
and it does defnitely cure the issue for a while, at least.

I've not had any further opportuinity to monitor what's happening when it
does occur (I bought a cheapo ELM 327 USB dongle for that purpose, but
haven't really had opportunity to use it, when I've encountered the
problem - either because of time, or location). I suspect I'd probably see
what I initially saw / logged - absolute throttle position at idle around
9%, after doing the Ali-shuffle with the IACV plug, probably staying at 0%
at idle.

Reading the thread about a Fiesta having an idle problem, here, makes me
wonder about ECU adaptation and the TPS. I enquired at my local dealers, and
a TPS seems very reasonably priced, so I've ordered one, and hope to fit it
in the next day or two.

If it is a potentiometer type TPS, they are quite easily checked. Best
with a scope to see any noise on the track while it operates, but a DVM
can show up problems. They normally wear most at the closed end.

Other way is to wire it up as a volume control between say a CD player and
amp. Any problems with the track will be easily heard as it is moved.

--
*Stable Relationships Are For Horses.

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Only thing to report is that I changed the TPS (it cost something like
£23-24 for the OEM part from a dealers, I think even the aftermarket costs,
or costs of the OEM part from the far east were more expensive).

Changing it was reasonably straighforward - although I would say that access
to the retaining bolts are awkward for both this and the IACV (removed to
make it easier to remove the TPS) - both rearward facing, and between the
rear of the engine and the bulkhead at the back of the engine bay.

One thing I noticed from the part I took off (identical to the new one, so I
suspect it's never been changed previously), is that the default position
for the inside of the TPS (ie where it comes to rest) once removed, seemed a
fair bit different from the brand new one. Whether it was prone to sticking,
or there was any roughness in the track causing it to not fully return to
the same position as the brand new one, I'm not sure.

With everything connected up, the car started fine and idled completely as
you'd expect (although not really proving anything). I let the car fully
warm up, but didn't have chance to drive it (on account of needing to stay
at the house when I had chance to do the job). I've not had chance to drive
it, yet, but when I've managed a few days driving in it, I should have a
good feeling as to whether it's made any bearing on the problem.

Hopefully, final feedback on this.

My previous reply, where I'd fitted a new (OEM) TPS, seems to have done the
trick. I've not driven that much in the weeks, since, but have done a fair
few local journeys, and 3 or 4 commuting round trips (60-ish miles each way)
and had no reoccurence.

Before changing the TPS, I would have definitely had an incident of it. So
whether it was a combination of heat / warm engine and a TPS playing up at
closed throttle position, or a warm engine / engine-bay causing the TPS to
give odd readings at closed throttle, I'm not sure, but so far (fingers
crossed) a new one has done the trick.

I've not yet had chance to plug my laptop and ELM dongle in, yet, but I'll
be interested to see if there's a notable difference to when I'd logged
metrics when it was playing up.

I'm sure I'm not alone in hoping I don't have to post any further replies
about the problem returning!

On Fri, 09 Sep 2011 16:34:08 +0100, Lester Burnham wrote:

[...]


Glad it seems sorted; it's actually these tricky-to-fix problems that
usenet is most useful for.

It certainly not been the worst thread on u.r.c.m by a long way...

Chris

--
Remove prejudice to reply.