RPM shooting up at start up

[Bossxr8]

My daughter has a 2005 Focus petrol auto. On start up the revs shoot up to about 2000 rpm for 3 or 4 seconds, before it drops back down to a normal idle. No fault codes showing up.

Any idea what it might be causing this? Drives fine all other times.

I'm assuming it would have an electronic throttle body?

[auc-05l]

had this issue. its the hose connecting the pcv valve to the manifold. probably split. bastard of a job to fix as the inlet manifold has to come off. hows your fuel economy?

[Bossxr8]

Originally Posted by auc-05l

had this issue. its the hose connecting the pcv valve to the manifold. probably split. bastard of a job to fix as the inlet manifold has to come off. hows your fuel economy?

Was it intermittent? She reckons it only happens from time to time.

Is the hose easily visible? Might have a look at it and see what sort of condition it's in.

[auc-05l]

no it happens everytime once the engine is warm. hose is very hard to see as its under the intake manifold. between runners 3 and 4. you can just see it between the runners.

[Metdevil]

Originally Posted by auc-05l

had this issue. its the hose connecting the pcv valve to the manifold. probably split. bastard of a job to fix as the inlet manifold has to come off. hows your fuel economy?

Definitely this. Happened on my 05 Mondeo (apparently very similar to the Focus). And yes, it is a nasty job. You might be able to see the split if you know where you're looking and might even be able to feel it if you have small enough arms.

We found on the Mondeo that it only happened on start up when the engine wasn't warm. Leave the car for a few hours and it would do it again.
You could see what was happening once you get the hose out, on start up you get a massive vacuum leak until the hose sucks the cut part inside itself, basically making itself G-shaped. Once the wound is closed, you're back to metered air and it's like it never happened.

Here's a picture of my hose, with the new hose installed onto the manifold on the right: https://drive.google.com/file/d/1iaR...ew?usp=sharing

Might also pay to get yourself a new PCV valve while you're in there too.

[auc-05l]

Originally Posted by Metdevil

Definitely this. Happened on my 05 Mondeo (apparently very similar to the Focus). And yes, it is a nasty job. You might be able to see the split if you know where you're looking and might even be able to feel it if you have small enough arms.

We found on the Mondeo that it only happened on start up when the engine wasn't warm. Leave the car for a few hours and it would do it again.
You could see what was happening once you get the hose out, on start up you get a massive vacuum leak until the hose sucks the cut part inside itself, basically making itself G-shaped. Once the wound is closed, you're back to metered air and it's like it never happened.

Here's a picture of my hose, with the new hose installed onto the manifold on the right: https://drive.google.com/file/d/1iaR...ew?usp=sharing

Might also pay to get yourself a new PCV valve while you're in there too.

yep thats what mine looked like. i got my hose from overseas as ford wanted $120! pcv valve was a much more reasonable $24 from ford.

[Metdevil]

Originally Posted by auc-05l

yep thats what mine looked like. i got my hose from overseas as ford wanted $120! pcv valve was a much more reasonable $24 from ford.

Can't remember what mine set me back, but I think it was only about $20.

Also, I think some models have plastic swirl plates in the manifold which can break off and go through the engine (mine didn't), so if yours does, it might pay to just check the state of them while the manifold is off.

Here's a pic: https://www.robert-jenkins.co.uk/mon...old-port-1.jpg