ford focus 1.6 vetec intermittant eratic idle

[audiv10power]

Hi guys/girls I have a ford focus MY 2000 1.6 vetec which drives ok but intermittantly has eratic idle there are no DTC in the engine control unit I have replaced spark plugs and removed the idle control valve and cleaned it has anyone got any ideas or have had this problem before ?

[Andoo]

If it was running rich, there would likely be a stored code, so it's possibly running lean.

Check for air leaks at the inlet or perhaps perished rubber hoses.

[fatjon]

servo vacuum pipe split, classic fault one these cars.

[audiv10power]

ok vlaid point about an air leak but why would this be intermittant?

[fatjon]

Afraid I can't answer that one but it is a fact none the less. My neigbours car had this problem last month. Big split in the servo pipe. Intermittent high rough idle and frequent stalling when coming to a halt with the clutch dipped.

[Andoo]

I can only imagine that temperature variations have an effect on the size of the hole!

The trouble with intermittant faults is that....well, they are hard to find

I remember Rover/BL cars had some fault with pipes hanging low and filling with oil or petrol which created havoc with some ECU sensors due to a lack of vacuume.

Keep looking for small splits.

Another possible problem is damp mornings covering the Hi Tension (plug) cables and causing a short circuit which can also create such a problem.

Best time to look for this is in the dark with (Headlamps OFF) the bonnet open and look for a miriad of small sparks.

[audiv10power]

The problem is not a misfire and it only happens on idle when stationary and when it happens if you just raise the engine speed by 50/100 rpm it stops and will only happen again if you let it go back down to idle its starting to do my head in

[Andoo]

Something at the back of my head is nagging about this erratic idle so I looked....and I found this:

Problem: Intermittent high idle and noises.

Solution: The probable cause is acoustic resonance of the IAC (Inlet Air Control) system. The problem can be rectified by fitting a new revised intake manifold, distributor vacuum hose and crankcase vacuum hose. A revised intake manifold has been fitted since 08/2000.

Hope it helps.

[Mr2Mike]

audiv10power said:

Hi guys/girls I have a ford focus MY 2000 1.6 vetec

Zetec perhaps?

A failing VSS (Vehicle speed sensor) causes idle problems on the Focus, and is an very common fault. Have you ever seen the speedometer flick down to zero briefly whilst driving?