My brothers 1.6 focus has just started developing a bit of a weird issue.
As a whole the car runs absolutly perfect. However on pulling up at traffic lights its begun to start hunting, ie the revs go up and down a few hundred RPM, then drop, then raise again.

Dont really know what to suggest for him, its got all new plugs/filters and stuff. Any ideas what this maybe is.

 

iscv: idle speed control valve could be gunked up. order a new gasket for it and clean out with some carb/brake cleaner

 

yeah zetecs normally have this problem, clean, or change the idle speed control valve, its underneath the inlet manifold i think on the black manifolds.

 

Ah cheers guys, will drop him a text.
He does look after the old girl, and is always serviced.

 

As already said

 

So my brothers done the plugs, the Idle control valve and still doing it.
Asked him to leave the ecu disconnected for a few hours but its still doing it.
Any other ideas guys?

 

Up up guys!

 

torch it.

 

when you say "done" do you mean he put a new iscv in or just sprayed it with oil?

 

ive seen a few mk1 focus's suffer from vehicle speed sensor (vss) problems, this can cause it to hunt when pulling up at junctions and even cut out, has he noticed the speedo drops to zero when he is driving at all? as this can also be vss related.

 

It was a new Idle speed valve.

RS20004X4. Very interesting. He had issue with the speed sensor a couple of months back. However it just stopped playing up....

 

Mine does this, does it worse / moreso when more electrical things are on, sometimes stalls.

I cant use the lights wipers and my headunit at the same time or the car will stall

 

could be pcv. this is also known to cause issues especially with soft or split pcv pipes. meant to vent some pressure to atmosphere to prevent stalling and is known to cause erratic idle if pipes are split or collapsing

positive crankcase ventilation valve