My 2001 Focus 1600 Zetec petrol has developed an annoying issue with idling.
It became 'lumpy' with an inconsistent idle speed, with the rev counter
needle twitching around, sometimes jumping up to 1100 rpm, and occasionally
settling at around 750 rpm. A few times, when dipping the clutch after a
high speed run, the engine cut out altogether but restarted easily.

After the local mechanic tested it via the computer port and said there was
nothing showing up, I was advised to replace the ISCV, which I thought was
worth a shot for 45 quid for a genuine dealer part. After fitting (and
disconnecting the battery for a while to force the ECU to 'relearn'),
everything seemed great once I'd driven it for a few miles- steady, smooth
idle and no alarming dips in idle speed when dipping the clutch. So I
thought it was fixed- wrong!

After being parked up for a couple of days I took it out today and it's back
to its old tricks, though not quite as bad. Drop the clutch and the idle
drops to about 200rpm briefly, and when idling there's sometimes a
rhythmic 'hunting' effect, which can be both heard and felt. Also, the idle
speed will sometimes jump up to around 1000rpm for a few seconds for no
apparent reason. It definitely feels better to drive, but obviously the
idle problem needs rectifying.

Can anyone shed any light on other possible causes please? I read somewhere
the throttle body can become contaminated and need cleaning, causing
similar symptoms, but I don't want to randomly pull out parts and fiddle
with them unnecessarily.

Thanks

Morse

"Morse" <morse (AT) 248rpa (DOT) com> wrote

Check the output from the TPS around the idle position, and jumps or
glitches, replace it.

Tim..

Tim.. wrote:

Tim, thanks for your quick reply. Is this best done with an oscilloscope or
can it be done with an analogue multimeter? I have both but obviously a
meter would be more convenient :-)

Morse

"Morse" <morse (AT) 248rpa (DOT) com> wrote

If you have a 'scope- use it- is more likely to show up a dirty output.

You are looking for a 0.7v output or there abouts with the throttle at rest,
rising smoothly to ~4.5v WOT. (key on)

Thanks Tim, that's great info! I'll have a look when it comes back from the
paint shop next week. It's typical that it acts up on the way to the damn
garage so i can't take a look at it for another week!

Dave