VR6 - Revs surge during gear changes up.

[craigowl 0]

I don't really know if this is a problem. It may not be.

If it IS a problem, I dont know if the problem is with me, the Corrado, or other cars that I have driven.

I have noticed that, since I got the Corrado over 2 years ago, when I am pulling away and going up thro the gears in the way most natural to me, the rev counter surges between gears. It doesnt go up by several thousand revs, or by anything that causes an unusually excessive engine noise, but the instrument dial certainly shows it happening.

By altering the timing of the clutch/accelerator operation in a conscious way I can eliminate the surge as I watch the dial, but I feel the gearchanges are too slow and stilted then.

VW garage and my local garage man, (an ex formula Ford racing driver and Ferrari owner) both said they could find no fault with the car's operation. But if you dont look at the rev counter, you certainly wouldnt.

As with most C owners I am probably being over fussy, but it would be interesting to hear from others.

The cars fuel economy is brilliant - 27mpg on the worst stop start journeys and 34mpg on a recent 200 miles plus run to the Highlands and back.

The other car I mostly drive (for 12 years) is a Peugeot 205 1.9 Diesel with no rev counter.

[kangaroo 0]

Funny you mention it! I've noticed this too, but I put it down to sloppy gear changes on my part. Its only a subtle rise, as you say, sometimes not even a rise but I feel the revs should be dropping a tad quicker.... Maybe its just the Corrado style... I can't remember back to the others I test drove, and its certainly going to be a lot different than my old MKII Driver, so maybe I should just get used to it.

[dr_mat 0]

Perhaps you have a sticky throttle cable, or a clutch that's a bit worn? The clutch should self adjust but if it's on the verge of slipping, the slightest touch on the pedal will allow the engine revs to rise.

[DaveStorm 0]

Mine does this too metman. I also time my clutch/accelerator operation to try and stop the surge but sometimes it feels like it takes forever to change gear, is this *yet another corrado quirk*?! I wonder if it could be a coincidence that the problem affects your car, kangarooboys and mine, which all happen to be some of the last of the VR6s?

[craigowl 0]

DaveStorm and Kangarooboy thanks for your input.

I now think it may be idiosyncratic of the car - or a Corrado quirk - as Dave terms it.

I seem to remember reading something on this forum that made me think the rev surge could be a mechanism to prevent unburnt fuel screwing up the catalyst. Don't ask me to explain the physics - it was just something that twigged when I was reading remarks about the engine's behaviour.

 

drmat - thanks for your info. Im not convinced that the clutch is a problem - it has good bite. Also, it was renewed during previous ownership. Neverthless, I will not dimiss your suggestions out of hand for the time being. Anyway, as you have a late VR6 do you not see an increase in revs on the tachometer between gear changes (up)?

Regards

Iain

[VR6 0]

Got to say that I notice it sometimes, but I think that could just be down to changing too fast and the revs not having chance to drop properly.

 

I'd certainly think about chaing the throttle cable anyway. Certainly won't assist a slick gear change.

[Joe M 0]

I'll say throttle cable too, I had this to an extent when I bought my vr6, new throttle cable cured it.

[craigowl 0]

Thanks, Joe and VR6.

Probably good time to renew throttle cable next opportunity.

[kangaroo 0]

Sticky throttle cable? Hmmm.... When I'm crawling along in a queue at low speed, (say in first or second gear, 1.5-2k revs), and I gently lift off the throttle, the car will not doing anything for half a sec then suddenly lurch dramatically and slow down. Sometimes its the same if I push the pedal down to accelerate. Do you think that's another symptom of a sticky throttle cable? Do yours do this at all, metman and davestorm?

[yellowslc 0]

Start with throttle cable... mpg indicates no issues with fueling/metered air/ignition.

 

R

[craigowl 0]

Thanks guys.

kangarooboy said

the car will not doing anything for half a sec then SUDDENLY LURCH DRAMATICALLY and slow down. Sometimes its the same if I push the pedal down to accelerate. Do you think that's another symptom of a sticky throttle cable? Do yours do this at all, metman and davestorm?

Mine doesnt do anything odd apart from indicating a rev surge between gears going up.

Now I know why you are called kangarooboy, Matt.

[DaveStorm 0]

Thanks guys.

kangarooboy said

the car will not doing anything for half a sec then SUDDENLY LURCH DRAMATICALLY and slow down. Sometimes its the same if I push the pedal down to accelerate. Do you think that's another symptom of a sticky throttle cable? Do yours do this at all, metman and davestorm?

Mine doesnt do anything odd apart from indicating a rev surge between gears going up.

Now I know why you are called kangarooboy, Matt.

 

No Matt mine doesn't do this either, might try fitting a new throttle cable to see if it improves things though :wink:

[yellowslc 0]

matt.. maybe you should find a spare instrument cluster "clocks" to swap in and see if there is where your problem is. Actually, first check the resistance throughout that entire circuit, you may have a corroding wire and/or connection.

 

R

[dr_mat 0]

the car will not doing anything for half a sec then SUDDENLY LURCH DRAMATICALLY and slow down.

 

There is a damper on the throttle body to prevent the butterfly from slamming shut in the event of you lifting off suddenly. It should gently lower the butterfly closed, THIS is why at very low revs/small throttle openings you notice this kind of behaviour. The engine is on it's normal program, so it's providing fuelling, and then you lift off - you've got a lag on the throttle closure, when this lag finishes, the engine switches straight to overrun program, i.e. almost no fuelling. This makes a big difference at low revs...

 

Or something like that.

[Robbo149 0]

Yeah, the dashpot stops the throttle from snapping shut as dr mat says. It's the little plunger thingy underneath the throttle lever thingy (excuse the terminology). These can be prone to sticking & cause problems with revs rising & falling. Mine was sticking in & causing the revs to drop too fast sometimes. I suppose if its sticking out it could maybe have the opposite effect.

 

Cheers,

Robbo

[craigowl 0]

Robbo149 said

Yeah, the dashpot stops the throttle from snapping shut as dr mat says. It's the little plunger thingy underneath the throttle lever thingy (excuse the terminology). These can be prone to sticking & cause problems with revs rising & falling. Mine was sticking in & causing the revs to drop too fast sometimes. I suppose if its sticking out it could maybe have the opposite effect.

I think I know the plunger thingy you are referring too. How do you check for and stop the sticking Robbo149?

[craigowl 0]

Attention dr mat.

Do you get the surge? (or is it just the way you are standing?)

[dr_mat 0]

I refuse to answer that question on the grounds that it may incriminate myself... ;)

[Robbo149 0]

metman - I just gave mine a quick squirt of the old WD40 and pushed & pulled it in & out repeatedly (this thread really is getting silly isn't it?) this seemed to free it up ok. AFAIK they can be bought as a separate part if it's sticking really bad. You'll need to pull the throttle cable cam out of the way, probably easiest to disconnect the cable. I did mine with the manifold etc off the car.

 

HTH,

Robbo

[kangaroo 0]

Okay, my dashpot plunger thingy seems ok, its not visibly sticking. I'm gonna go with a new throttle cable i think. It seems the obvious repair choice given the cost.

 

So how do I set the new cable up? How much tension does it need? How immediate should the throttle response be? At the moment there's probably a good few millimeters of pedal-press before anything happens..

 

Cheers for the advice!

[Kevin Bacon 5]

I set mine up with no slack initially and it was a like a hair trigger! You want a little bit of slack... One or two notches worth on the cable adjuster.....

 

You might find your new cable is stiffer than the old one initially, but it should work loose......

[kangaroo 0]

Thanks for the reply Kev! I'll endeavour to get a new cable fitted in the next couple of weeks.