A few months back the engine developed a fault where the idle was
rough/hunting rhythmically, and then the idle would either intermittantly
stick high after releasing the accellerator, or cut out, the latter
especially after a high speed run.
A local mechanic kindly looked at it for free with his code reader and said
there were no fault codes, and that the most likely cause was the ISCV, so I
changed it at around 45 quid, no improvement at all. After some head
scratching and a helpful tip over on alt.autos.ford.focus, I changed the PCV
valve for about 3 quid which cured the cutting out and high idle completely,
but the hunting/rough idle remains. I have removed the battery to reset the
ecu, still no joy.
The symptoms are more pronounced when cold- is goes from about 1100 to 1200
rpm over and over at around twice a second. When the car warms up it settles
to normal speed but keeps dipping slightly at the same rate. Sometimes it
feels it has dipped so slow it would stall, but recovers in a repeating
cycle. ISTR once when it did this really badly it sounded rather like it was
dieseling briefly when it was at the slowest of its cycle, which made me
wonder about insufficient fuel pressure, but its on-road performance doesn't
really fit with this.
Another strange thing I noticed was when gradually increasing the revs in
neutral there comes a point when the revs actually drop a couple of hundred
rpm, despite opening the throttle further, then keep opening the throttle
and it picks up normally again. IIRC this happens around 3000-3100 rpm. This
made me suspect the TPS, but I stuck my 'scope on the output and the level
keeps increasing smoothly as I open the throttle even when the engine slows,
which made me think I was on the wrong track.
Common faults I've seen mentioned on Focus forums are the EGR system and the
MAF sensor. Unfortunately (or fortunately, depending how you look at it!) my
car has neither, it is equipped with a MAP sensor on the end of the
manifold. As this seems much rarer than the MAF version it isn't easy to
find tips online so I'm lost.
The car has done 61000 miles, the air filter is clean, fluids are correct
etc. I've checked the obvious stuff like blocked PCV/ breather hoses, and
I've removed and checked the throttle body for carbon build up and leaks.
The car starts normally, the exhaust is clean and the plugs are virtually
The car sometimes performs quite well, sometimes is a bit sluggish. It can
be twitchy at low revs/speeds and sometimes surges a little making for a
jarring ride. I usually have a very smooth clutch action but the car 'pulls
back' on changing up gears which is very annoying. Once it's in top gear and
on the open road it is smooth.
My last resort here is changing the MAP sensor, which is only around 40
quid, but money is tight right now so I'd appreciate any advice prior to
going for a 'suck it and see' repair approach.
Thanks in advance for any help.
Have you checked the rubber T-piece down behind the coil? Apparently it
often splits and when it does you get a poor idle, stalling, all the things
a vacuum leak usually gets you.
A few quid from a dealer.
In message , PC Paul
It doesn't have one. The engine in the 1.6 Focus is a completely
different unit to the early Zetec E silvertop in the Escort/Mondeo that
did have the rubber T piece. Even in the Mondeo, the T piece was omitted
from 1997 onwards.
Do you suspect a vacuum leak, Paul? I couldn't find one, but I could have
missed something of course. There's definitely no leaks in the PCV system,
and I plugged any vacuum hoses coming off the inlet system as a test. It's
very frustrating and it looks like I'll have to save up and bung it in a
'Suspect' is too strong a word - it's just that that T piece causes the
same sort of symptoms, is easily overlooked and is a quick cheap thing
to try. But if you haven't got one...it probably isn't that ;-)
Zetecs are all hard on the leads (Ford OEM are always recommended), and
do you have the plugs set to 1mm as I believe the manufacturers setting
makes the leads plugs and coils work way too hard?
That's interesting, and come to think of it, when I pulled the plugs out I
noticed they had what I thought were huge gaps. They weren't dramatically
wider than the spec but the gap still looked big! IIRC it was around 1.3mm.
I regapped the plugs with no improvement, but perhaps it would be a good
idea to change the plugs and leads and go from there. I'll regap them to
1mm first though as it costs nothing!
Thanks for your help, it's much appreciated.
Cheers, I'll go with the genuine Ford gear, but how much is not
cheap? I have no idea at all of prices as I've never bought HT leads
before, despite owning cars for 21 years! I take it the carbon core breaks
down over time?
The leads are around a tenner each, I'm afraid.
Yes, failure of the carbon impregnated core can happen; also poor
connections where the conductor connects to the termination is common.
BTW, if you are interested, there is a dedicated NG for the Focus at
Oh well, could be worse I suppose. I was going to change the TPS and MAP
sensor anyway so it's not so bad!
Thanks Chris. The original problem was solved there by a helpful chap called
Tim who advised checking the PCV system. There's far more traffic here
though and it's UK specific so I thought I'd try this group this time
Correction- it does this when it hits 2000 rpm. It keeps doing it with no
increase in rpm despite pressing the accelerator further down. The engine
really sounds like it's struggling. Eventually the accelerator reaches a
point where the revs pick up freely.
Another thing- if I reset the ECU and force it to re-learn, it runs a lot
smoother and accelerates better from a standing start- until it completes
the re-learn then things are back to its old ways. Even during the brief
performance improvement it still idles badly when cold and the 2000 rpm
'wall' is still there, though hot idle is temporarily improved.
Still think you have an air leak... The ISCV is mostly responsible for
engine power in the first 1/4 of throttle movement- certainly upto around
3500rpm off load- after which time the throttle disk plays more of a part.
Are you sure the manifold gasket hasnt sucked in and that the intake rubber
hose is split free- take it off, and stretch it whilst looking inside at a
Thanks Tim, I'll give it another good going over, I may well have missed
something first time round. Actually- there's one component which appears to
be attached to the air intake via a hard plastic pipe via a rubber grommet
type seal (which is a little cracked but no sugn of a leak). It leads to an
odd looking circular plastic box on the bulkhead which has another similar
plastic pipe attached which disappears off somewhere, and there's a small
box attached which resembles a relay with a wires coming off. Do you know
what it is and whether it could be the source of a leak? I can't work out
how to detach the pipe from the intake to plug it for testing, or even
whether I should do this in the first place!