Ford Focus Engine revving by itself

Mike pretended :

No doubt other suggestions will follow, but I would suggest-

1. A vacuum or intake leak somewhere.
2. A sticky IACV (idle valve). These just bolt on to the intake manifold with a couple of wires plugged into them. Give it a good spray with carb cleaner to get the gunge out, then some thin oil on the moving parts.

Cleaning the IACV is often only a temporary cure; replacement is a much better idea, especially on this engine where the usual means of access is to first remove the inlet manifold.

Chris

This 'idle flare' is a design "feature" to minimise emissions during warm up, BUT yours should not be revving as high as 3500rpm.

We need to know if it does this when the car is moving (eg clutch dipped approaching a junction) or when stationary, or both, as the remedy is different.

Also if it happens when the clutch is dipped, does the revving drop immediately the car comes to a halt, or does it continue?

Tim..

There is probably a pressure switch on the power steering lines that is there to prevent stalling when steering at low revs (e.g. parking). If that has a dodgy connection it could make the ECU rev the engine. I had this problem on a Zetec Fiesta engine and it was a bugger to track down.

Still, I have a spare IACV and a spare TPS now :-)

Tony

Tim,

At happened tonight as I was approaching a junction. I pressed the clutch and the revs stayed at about 3000 as I braked. The engine continued to rev as I came to halt and stayed at about 3000 revs. I then blipped the throttle, the revs went up to about 5000 and back to tickover and it never did it again.

If it helps, the car had been standing all day so it was completely cold, this was after leaving work and I had driven about 2 miles. The rest of my journey (another 20 miles) was fine. It has never done it when the engine is fully warmed up.

As far as I can tell, the engine isn't doing anything else strange. No loss of power, no clouds of smoke out of the back, it's not using more or less fuel than it has before and it isn't using any oil or water.

Mike

Mike formulated on Thursday :

Hmmm.

Could this be a faulty throttle position sensor?

I would check the TPS voltage at idle- if it is over 0.7 then you are going to have problems with idle flare.

If it appears ok, check the throttle body for dirt, and then look at replacing the ISCV. (not the easiest of jobs!)

Tim..

There is a TSB if memory serves for early engine that were fitted with a Mondeo inlet manifold that resulted in high revving an a reluctance to drop. 3500 sounds a little high for a stuck ICV.

There was, but that was only for the 2.0 Zetec-E's.

Tim.