Turbo owners...

Shure · 19 Nov 2007 at 20:51

Would you say it is normal for a turbo'd petrol engine to raise the revs(on its own) upon a gear change before lowering to where it should be with a recirculating dump valve?

Might sound a silly question to some of you but I'm getting mixed answers :confused:

BigglesPiP · 19 Nov 2007 at 20:54

Lets get the facts straight: It revs up when you press the clutch? Or some time after?

arcamalpha · 19 Nov 2007 at 20:54

Yes, cos there will still be some boost in the system when you drop the clutch (esp if you still have your foot on the accelerator). The boost may well be enough to raise the revs a touch when the clutch is in.

L0rdMike · 19 Nov 2007 at 20:56

Mine never raised the Revs when changing gear.

arcamalpha said:
(esp if you still have your foot on the accelerator)

That would cause the revs to raise.

Shure · 19 Nov 2007 at 20:58

BigglesPiP said:
Lets get the facts straight: It revs up when you press the clutch? Or some time after?

If the turbo is boosting around 3k rpm and then I change gear, as soon as my foot hits the clutch (my other foot is not on the accelerator) the revs will rise usually around 500rpm.

If it helps I drive a mk4 golf 1.8T

EDIT: the main reason I ask is that I have just had a clutch pedal replaced and the master cylinder along with a 80k service(sparks etc) and since then it has started doing this.

Stonedofmoo · 19 Nov 2007 at 21:02

arcamalpha said:
Yes, cos there will still be some boost in the system when you drop the clutch (esp if you still have your foot on the accelerator). The boost may well be enough to raise the revs a touch when the clutch is in.

Eh

nutcase · 19 Nov 2007 at 21:04

Can't say I've ever noticed mine doing that.

Freefaller · 19 Nov 2007 at 21:04

Can't say I've noticed it.

djbenjo · 19 Nov 2007 at 21:05

arcamalpha said:
Yes, cos there will still be some boost in the system when you drop the clutch (esp if you still have your foot on the accelerator). The boost may well be enough to raise the revs a touch when the clutch is in.

Erm dont think so mate.

Doesn't sound right to me tbh, sticky throttle cable?

Pants · 19 Nov 2007 at 21:06

Can't say that my 1.8T does the same.

And it's not down to there being boost left in the system, because once your foot comes off the throttle the throttlebody is closed. Even if there is still pressure there, it won't get past the throttle body.

Some ECU's do hold the rev's for a while after letting of the throttle though, as a feature to smooth any abrupt throttle movements and make for a more comfortable ride. It also saves on engine mounts. It could be that your ECU does this?

panthro · 19 Nov 2007 at 21:07

mine does very slightly, only 100 rpm or so, dunno why it does it.

gurusan · 19 Nov 2007 at 21:08

Definitely shouldn't be doing that. You want the rpms to fall, not rise.... so that you can drop into the next gear easily and quickly.

Possibly some sort of vacuum problem? I'm not sure you would notice something like that above 3000rpm though.

beats me

milgo · 19 Nov 2007 at 22:28

I only really know old engines. But if there is a leak on the inlet mannifold the car will tend to rev on when you take your foot off the accelerator because the engine is still able to suck in additional air as if the throttle is slightly open.

Like gurusan says id check for a vacuum leak.

Lopéz · 19 Nov 2007 at 22:30

The revs should rise when you dip the clutch to change gear. Is the throttle sticking?

g60dubster · 19 Nov 2007 at 22:50

what year golf, is it cabled throttle or drive-by-wire?

Sounds like sticking throttle pos sensor.

ScoobyDoo69 · 19 Nov 2007 at 23:00

panthro said:
mine does very slightly, only 100 rpm or so, dunno why it does it.

Yup scoobs have the tendancy to do it. Every one I've been in has done it.

BigglesPiP · 19 Nov 2007 at 23:20

Probably because the bite point is higher on the clutch pedal, and there is now less time between you letting go of the throttle and releasing the clutch.

Shure · 20 Nov 2007 at 07:39

g60dubster said:
what year golf, is it cabled throttle or drive-by-wire?

Sounds like sticking throttle pos sensor.

DBW if I remember correctly? Engine code - ARZ(late 2000)

Hawk Tuah · 20 Nov 2007 at 08:37

Not mine. Foot off accelerator / clutch in = revs go down.

Sounds like your throttle is sticking.

Dogbreath · 20 Nov 2007 at 10:03

BigglesPiP said:
Probably because the bite point is higher on the clutch pedal, and there is now less time between you letting go of the throttle and releasing the clutch.

I agree, sounds by far the most likely cause if any clutch components have just been replaced.

As said some cars (notably later Fords) do have this (hugely irritating) feature built in.