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Juddering when Lifting off

Hi Jeff

I checked the Pedal area Saturday and the cable is very free. Can't get to the other end to see if free on the throttle body unless you know how to get to it?

ISV is clean and free now too. Just waiting to get it booked in for Diagnostic check etc

Was hoping to find the fault 1st thou!

Graham

 
Graham,

I'm not sure whether or not your 993 has a "drive-by-wire" throttle actuator arrangement. If so then the cable from the pedal will only operate a pedal position transmitter [potentiometer] which then sends a signal to the DME to operate the throttle, dependent upon demand. I think your tech will need to use the diagnotic kit to ensure that the system is operating correctly.

Jeff

 
Jeff

All I know is the cable leaves the footwell in the tunnel towards the rear of the car

See here! [link=https://drive.google.com/file/d/0B7ErqWl2I-7ONG5EbEx2bnBpQW8/view?usp=sharing]
view
[/link]

Graham

 
Graham,

It certainly looks as though the throttle is cable operated but I've just found this link which should be useful when your tech hooks up the diagnostics:

Throttle position on the 993 is monitored by a potentiometer - this feeds back to the DME so that once more than 1 degree is registered it switches off engine idle settings. It operates 'full load' at 66 degrees of throttle movement. WOT on the 993 (throttle fully depressed) is 84 degrees +/- 3 on the actual values menu Throttle in release position should read 0 degress on the actual values menu. If you have durametric software and cable then you can set these up correctly.

A faulty potentiometer could be a potential source of your erratic engine idle problem. However, I fear that if everything checks out OK you may have to bite the bullet and remove the engine and transmission to check the clutch, DMF, driveshafts and powertrain mounting system.

Jeff

 
Used my Bergvill OBD tonight to check for any fault codes etc. No fault codes found which is good

Did the Throttle Position test. There are 2 Videos, sorry they are not that clear to read. 1st Item on the screen "Thottle Angle"

Video 1 is as described below Click Here>[link=https://drive.google.com/open?id=0B4Jf1F4qCNcSLVZ3QUx2NW1lalE]
view
[/link]

No foot on Pedal is -0.84 Degs

Foot hard on full Pedal 84.84 Deg

Video 2 is as described below Click Here>[link=https://drive.google.com/open?id=0B4Jf1F4qCNcSNGRtWldtVmVsYU0]
view
[/link]

Here is a Live test with rev Counter and OBD Software together. Again sorry it's not that clear filming the computer screen

Can't hold the revs at any point where I want. Pedal still but revs keep climbing

You will notice that the live data doesn't seem to change with the revs either

Could this be a faulty potentiometer?

Thoughts please

Thanks

Graham

 
Several years ago I had a similar idle problem and went down the route of cleaning the ISV which didn't really fix it. Eventually it was discovered that the air filter was blocked with gunge from the breather pipe that comes up from the clutch bellhousing. My clutch was starting to disintegrate - I don't recall having any juddering but if your clutch is disintegrating this might be the cause of both of your problems. So worth checking the air filter. When my indy looked at the air filter it was so black he though it was some weird aftermarket product I fitted! It first showed up on the diagnostics as the air flow rate was well down and I think the engine management system was struggling to compensate.

Anton

 
Hi Anton

My clutch was replaced at 30k 11 years ago and only on 48k now so I'm pretty sure it's not the clutch.

it's been like it since I bought it but just though it was me. I know the main air filter is clean but will look into the clutch breather pipe

Graham

 
If the air filter appears clean then it's not likely to be the same problem that I experienced.

Hope you manage to get to the bottom it.

Anton

 
Sorry don't like abbreviations its under the inlet manifold right at the back of the engine

you will have to remove engine to gain access renew the throttle cable at the same time.

Have heard it is possible to drop the engine down and remove inlet manifold. that may give another can of worms.

Engine out.

Charles

 
Hi Charles

Thanks for that. Was hoping there was a way of getting to it by removing the airbox etc

Now need to workout what other jobs can be done whilst the engine will be out. Suggestions?

 
Graham,

It's a pity that you have to remove the engine just to access a minor component but at least you'll be able to check all the things I mentioned previously: transmission mounts [worth changing regardless], driveshafts and, if you split the engine and transmission, the DMF and clutch pack.

Hope you finally get to the source of the problem(s).

Jeff

 
Hi Jeff

Not really ideal having to remove the engine to replace such a small component but can't see who else to resolve this issues.

Will be at Porsche Swindon on the 16th Aug before Althorp so will speak to the techs there and quiz them on this issue too incase they have any other ideas!

Graham

 
A bit of an update

My car has been at [link=http://jgcporsche.co.uk/]JGC Porsche in Brackley[/link] for Bump stops, Front wishbone bushes and a look into the juddering

Bump stops both done and wishbones are done now also [:)]

James has taken the car out for a test drive and has felt the judder and thinks it might be the Dual Mass Flywheel but not 100% sure yet. He rang JMZ where the clutch was done at 30k 11 years ago before I bought the car and found it only had the clutch and not DMF done, so how could you be 100% that the DMF is at fault?

Graham

 
Sorry to hear that you're still being troubled by this problem Graham.

Unfortunately the only way to examine the DMF is to remove the transmission to enable the unit to be inspected for excessive movement and wear, so it'll be worthwhile making sure that the driveshafts and engine mounts are in good condition before going down that path.

Jeff

 
Hi Jeff

It is being a little frustrating! James will be back on it next week checking everything else before opening to check DMF

Graham

 
Maurice

Fairly sure they are good. The most noticeable thing which I can't compare as I haven't been able to drive someone else's manual 993 is when ever you lift off the throttle it is quite violent. Even more so at higher speeds. So for example your doing 70mph on a dual carriage way and as you lift off it isn't a nice smooth feel, it's more like you have hit the brakes if that makes any sense??

I'll be at the Club Christmas Open Day on the 6th Dec if anyone fancies and little ride with me to see and can take me out in their manual 993 varioram to see the difference??

Graham

 
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