Revs taking time to drop to idle

[Scion]

Car: 55 plate Mondeo, 1.8 Duratec petrol engine.

After pulling to a stop and disengaging the clutch the revs sit at 2k for
around 2 seconds, then drop to around 1.5k for another couple of seconds
before dropping to normal approx 900.

If I rev the engine when stationary (say to 3k rpm) then when releasing
the accelerator the revs drop to around 1.5k for a couple of seconds
before dropping to normal.

This has suddenly started happening and there are no other symptoms like
rough running, rough or hunting idling, or hesitation under acceleration.

I'm thinking either a leak in a vacuum pipe, or MAF sensor. I've only got
a short time over the weekend to look at it so any further suggestions
would be welcome.

[Mrcheerful]

yes, check for air leaks, try running it with the maf disconnected, but the
likely cause is the idle air control valve sticking, replacement is the only
reliable cure.

[Scion]

Mrcheerful put finger to keyboard:

I'd forgotten about the idle control valve. Is it worth blasting some carb
cleaner through it to see if it improves, or could that damage it? I'm
happy to replace it, but it would be good to prove that it's the problem
first!

[Peter Hill]

Take the assembly off and use carb cleaner, though the air ports. If you
can detach the actuator then the plunger can be worked at the same time.
If the coke is really bad then it needs swabs, pipe cleaners (took ages
to find someone that stocked them) or even use of a tooth pick but
nothing sharp and metallic.

--
Peter Hill
replace nospam with domain host name to reply

[Mrcheerful]

A clean up will not hurt it or make the problem worse. If it improves,
great.
I took one apart on my Focus 1.8 by cutting the ring that that keeps it
together, it can then be cleaned really well, it was then fine for a year or
so, it now needs to be replaced as the problem has returned.

[Scion]

Ta, that's what I'll do then. If it improves I'll probably replace it for
new anyway as I'm not planning on getting rid of the car yet.

[Scion]

Peter Hill put finger to keyboard:

Thanks for that. I'm just going to give it a very quick clean with carb
cleaner, if it improves it I'll replace the unit rather than faff around
with pipe cleaners when in reality I'm never going to get it really clean.

[Scion]

Hmmm well the clean-up did not make any difference, although I didn't take
it apart I just drenched it in carb cleaner and shook it around.

Can't hear any vacuum leaks.

Throttle cable movement seems smooth and returns to rest OK.

One thing I have noticed, which is probably very significant, is that if I
disengage the clutch with the car moving and coast along, the revs climb
high - 4k or more - and don't drop at all until a couple of seconds after
the car comes to rest.

[Mrcheerful]

That is the symptoms of the iacv. The reasoning is that it opens when you
accelerate and slowly shuts down after you take your foot off to improve
emissions, when it is dirty it is more difficult to shut down. I found that
I could get the idle to reduce more quickly by repeatedly pressing the
clutch down, but don't ask why. I ran mine around with the iacv
disconnected for a few weeks when it was running to over 5000 on its own, I
was turning it off while slowing down!!. get it running at a slightly fast
idle (say a 1000 or so) on its own (no foot on accelerator) and pull the
plug. It even went through an MoT fine. My one has been playing up
recently (a year or so after cleaning thoroughly) and I ordered a new one
yesterday. 43 quid delivered from the transit centre.

[Scion]

I'm surprised that cleaning the ICV had no effect but then not much crud
came out. I guess it doesn't take much to stop it working properly.

For £43 or thereabouts I'll just swap it.

[Scion]

Scion put finger to keyboard:

Presumably if I disconnect it and it still revs high that points to an air
leak? (Not done this yet but thinking ahead)

[Mrcheerful]

if you disconnect it while it is idling normally and it still revs itself I
would struggle to guess how !! try it, it does no harm, doesn't even put
the malfunction lamp on, but don't be caught out if it doesn't idle when you
expect, you need to learn heel and toe if it struggles to idle when
charging, ps operating etc.
On focus and mondeo they both had a problem with leaking vacuum pipes,
mondeo had a self destructing t piece and focus a hose that collapsed and
split, but both gave the symptom of a really poor or unreliable idle, not
revving.

[Scion]

My MK1 Mondy had the leaking t-piece, the air being sucked in made quite a
racket, of course a larger or different shaped split might not make the
same noise.

[Mrcheerful]

but still would have the same effect: if you add fuel at the split the
engine speed will increase. yours has already increased, so unless there is
also a corresponding fuel leak inwards there will be no speed increase.
in the days of carburettors an inlet leak did sometimes increase the idle,
but back then a standard CO setting was around 3 per cent (quite fuel rich),
modern injection stuff is around a hundredth of that, so there is no spare
fuel to get burnt.

[Mrcheerful]

I fitted my new IACV on the Focus and the running is all back to normal.

[Scion]

Ford want £86 for a new IACV, so I grabbed one from the scrappy for a
fiver. No difference whatsoever - although I have no way of testing the
replacement and it too could be duff. Also came off an earlier car,
although the engine looked the same (4 pot Duratec HE)

Your £43 one - is that trade or available to retail customers? I googled
Transit Centre and (unsurprisingly) got a breakers for Transits http://
www.thetransitcentre.co.uk/html/new_spares.html. Is that where you sourced
yours from?

I've seen them around the £40 mark on eBay but of course that's a gamble
if you don't know the seller or they have not been recommended.

Cheers

[tony sayer]

<Snip>

>I've seen them around the £40 mark on eBay but of course that's a gamble
>if you don't know the seller or they have not been recommended.
>
>Cheers

FWIW I fitted an ebay sourced idle valve to my olde Audi A6 and it never
ran right, course as it was a "new" one I assumed that it was fine and
OK and that something else was causing the problem..

Until I asked a local garage specialising in German cars. How much did
you pay for it they asked?, around 70 quid says I, well theres the
problem then. A gen VAG one will be at least 200 quid , furthermore
we've got a skip full of duff cheap Chinese pattern parts round the
back..

Fortunately I kept the old one, cleaned it out very thoroughly with
carb cleaner and Christ know what else.

Anyway fitted it back and its been spot on now for a year or so on the
cleaned up original valve .. the ebay one?. It went straight in their
skip;!...
--
Tony Sayer

[Mrcheerful]

The one I got was direct from an ebay seller, I fitted it the other day and
it now runs fine again, no over-revving.
The ebay seller is transitpartcenter . the one for mine was ebay number
321033474718
but I rang them direct on 0800 066 50 95 gave them my reg. number
and paid by card. 39.95 plus 3.95 post. came 36 hours later, fitted and
worked fine. sa...@transitparts.co.uk
BUT, mine is a 1.8 Focus, yours is a Mondeo. Hopefully they do yours if it
is different.

[Scion]

Thanks. After Tony's warning I've bitten the bullet and ordered from a
Ford dealer for £94. If it works, great, if not, I've spent nearly a ton
to have a small part of the engine valeted. C'est la vie.