Megane 250 revving issue

[Neal R19]

Anyone know what the problem is here?

This manifests in various annoying ways but the clearest way to demonstrate it is if I accelerate up to 2.5krpm, then hold the clutch down and foot off the accelerator, the revs bounce around right up to >2krpm until I'm doing walking speed, then they settle. Same in second. If I'm doing say 30 in 3rd then there will be a little bounce as it drops to about 1.5krpm, then it'll settle.

Asked on Facebook group and Mick (Diamond Motors) thinks (based on limited info) that it's probably a vacuum leak.

If I knock it out of gear as I put the clutch down it doesn't do it though, really odd!

Any ideas?

At about 4 seconds in the video as I hit 2.5krpm I put the clutch down and hold it and take my foot off the accelerator

 

[andybond]

Does it throw any fault codes?

 

[Neal R19]

No fault codes

 

[andybond]

I would wager that is an airleak as Mick said.

 

[Deleted member 486]

Air / vacuum leak sounds sensible - the only thing that would make me possibly hesitate might be the fact that it doesn't do it if you take it out of gear. When you take it out of gear do you leave your foot on the clutch or raise the clutch again?

It might be a clutch / gear position sensor with a bad connection. I know that quite a few cars try to "help" the driver when changing gear by holding engine revs to smooth the gearshift out. If this car has this feature then it a dodgy sensor could cause something like this as the ECU keeps trying to increase / decrease the revs.
It's more likely to be an air leak but maybe another thing to keep in the back of your head.

 

[Neal R19]

I had the same thought - seems odd that it only does it when moving above walking speed.

I even unplugged both clutch switches so it doesn't actually know where the pedal is... same.

I don't think there is a 'gear position' switch on the these? Only a reverse switch to operate the reverse lights?

 

[DaveL485]

There is an in-gear identifier because it wont start with the brake depressed when it's in gear.

Idle is controlled by the DBW throttle so i'd be looking at that and how its behaving. If it's an air leak it has to be behind the throttle butterfly too, so manifold gasket or injector seal. Doesnt really sound like a leak to me though it's not consistent enough.

 

[Neal R19]

Hmmm yeah that's a fair point.

The 'reverse switch' on these seems to be dual function



Maybe I'll piss about with that then and see whats what.