Juddering when Lifting off

[Motorhead]

That doesn't sound right to me Graham. An oversensitive throttle can't be help things but I thought you'd been down the route of checking that out.

I have to say that it does sound as though the engine mounts are struggling to control the motion but whether or not the problem lies with them is open to question. Chicken or egg?

Jeff

 

[Graham-S]

Hi Jeff

It's not being a easy one to say 100% it this or that.

I did find out that when the Clutch was changed before I had it at 30K the DMF wasn't done. Now why was the clutch changed at 30K????

The car needs it's 48K service next year so I am considering having the engine dropped and the DMF checked/replaced and the service should also be much easier with the engine out. Can get other little things done whilst out, eg plug leads, chain covers etc. Not going to be a cheap time thou!

Just hope someone might be there on the 6th Dec to help shed some light on my issues!

Graham

 

[chas3.2]

Hi Graham

I will be there on the 6 th you can drive my car.

 

[Motorhead]

A back-to-back drive in Charles' car sounds like a plan Graham and if you can hold off until the service is due then you can get the clutch, DMF, engine mounts and anything else checked out if you've not resolved the problem by then.

I'm hoping to be there on the 6th too, so might catch up with you then.

Jeff

 

[IndischRot]

I'm thinking the TPS should be checked. It really should read 0 when the throttle is closed otherwise the ECU doesn't think the throttle pedal is closed and the idle circuit is not activated. The D-shaped shaft from the throttle body engages in the TPS - this interface can wear and the TPS goes out of adjustment. The TPS isn't expensive, about £50 for a pattern part from Hella or the like. The same part is used on loads and loads of cars like Saabs and Vauxhalls.

I'm surprised the engine needs to be dropped to access it - on rennlist there are numerous posts about adjusting it to achieve a 0 reading and no mention is made of dropping the engine. I changed the TPS on my 993tt with no particular issue.

 

[Graham-S]

As it's varioram engine you can't get to it as its on the back of the engine, so there are 2 options

1) drop engine

2) removed induction / varioram kit

 

[IndischRot]

As it's varioram engine you can't get to it as its on the back of the engine, so there are 2 options

1) drop engine

2) removed induction / varioram kit

Ah, OK - I understand now. Thanks.

 

[Graham-S]

Nick from Redtek [link=http://www.redtek.co.uk/]http://www.redtek.co.uk/[/link] who works on Porsche aircooled engines for 25+ years drove my car and thinks it's the DMF

 

[Graham-S]

UPDATE

Last year I finally got the Clutch & DMF done along with the 24K service and all plug leads and rota Arms

They also checked the TPS, MAF and Engine Mounts whilst engine dropped - Reported All Ok

I'm afraid to say the juddering is still there! Now what????

 

[Motorhead]

How frustrating for you Graham, especially after all that effort - and expense..!

I'm just wondering: is there actually a clutch-like judder, ie a powertrain rotational effect, when you lift off the throttle or is it more like a fore-aft shunting motion? The reason I mention the latter is because I recall you saying that when you lift off the throttle the car decelerates very rapidly, which I suspect would induce snatch in the transmission resulting in fore-aft motion of the powertrain. The only way to cure that would be to introduce some damping in the throttle mechanism to achieve a more progressive throttle closure. [I presume you don't experience the problem if you come off the throttle slowly?].

Driveline shunt would also be exacerbated by wear in the driveshafts and backlash in the transaxle, but I assume these would have been checked as a matter of course during the work programme you've described.

I really do hope that you eventually get to the bottom of the problem.

Jeff

 

[Graham-S]

Hi Jeff

The Clutch doesn't judder it the engine/Car that does.

It is very hard to crawl in traffic as it's very hard to keep the throttle smooth. You seem to kangaroo it at times too.

Another example, you have been doing 60mph in 6th Gear and come into a 40mph, so lift off and slow down, put foot down to speed up a bit and when you lift off as little you can feel a judder, sometime very faint but after all this time I notice it easily. Change down to 5th, 4th or 3rd and accelerate and lift off, same again. Sometimes you can hear and feel the whole engine/gearbox moving back and forth like in the wrong gear. It's doesn't always do it/noticeable. It seems to be a little worse when cold, or that's how it seems.

I know that the diagnostic software for a 993's isn't very good at a live reading of the throttle position as it doesn't keep up quick enough

The car was in as Center Gravity before Christmas as it needed a tweak and they couldn't see any issues on the suspension side

My thinking as writing this is engine mounts and/or TPS but Porsche said they checked them!

Graham

 

[Motorhead]

Graham,

I have to say that from your description it sounds more like a throttle-related problem. If CG have given the suspension components a clean bill of health then I think that you can discount these as the source of your problem. Sometimes it's difficult to detect a powertrain mount fault without removing the item for a full examination. I don't know if it's necessary to remove the engine to change the clutch or if it's just a gearbox out job, so it could be that the engine mounts weren't looked at in isolation.

I don't know where you're located and if you're using an official Porsche dealership or Porsche Indy to do the work. Sometimes the dealerships lack technicians with experience of the earlier cars whereas certain Indies often have more experience in this respect. If you've not done so already, I can only suggest that it might be useful if you sought a second opinion from somewhere else in your area.

Jeff

 

[924Srr27l]

JEFF

How frustrating for you Graham, especially after all that effort - and expense..!

Driveline shunt would also be exacerbated by wear in the driveshafts and backlash in the transaxle, but I assume these would have been checked as a matter of course during the work programme you've described.

Gearbox sounds like the only thing left, does it have a LSD fitted?

R

 

[Graham-S]

It's a Standard 993. Don't know about LSD. Are they standard?

G

 

[924Srr27l]

It's a Standard 993. Don't know about LSD. Are they standard?

G

Option Code 220 is the LSD, I've just read your whole thread again and I'm involved now!! these things so annoy me as

they are so frustrating! It sounds like many things but unyet you've had most checked. Although with respect I'm a sceptic and

often some checks can miss things or not be seen as a fault but they are.

I'm not sure if the TPS is expensive? but ideally this should be replaced with a new one,

it does sound like driveline Shunt hence I wondered if the gearbox is at fault, although the throttle on and off seems to be also giving you the shunting and especially when you mention it's a pig to drive at slow speed in trafic.

How far are you from JZM ? they are very good

R

 

[Graham-S]

i'm 99% I don't have a LSD then.

I have been told to change the TPS you have to drop the engine or remove the whole varioram induction kit! Unless someone else knows different! It's right at the back of the engine

I am in Banbury M40 J11. I know where they are in Kings Langley, they just don't have courtesy cars or a least didn't and to get home meant the train but going to into London to go back up North!

I don't know how the garage tested the TPS to be honest either!

Here is a picture if the Throttle body with TPS located behind the Varioram Kit

G

 

[924Srr27l]

i'm 99% I don't have a LSD then.

I have been told to change the TPS you have to drop the engine or remove the whole varioram induction kit! Unless someone else knows different! It's right at the back of the engine

I am in Banbury M40 J11. I know where they are in Kings Langley, they just don't have courtesy cars or a least didn't and to get home meant the train but going to into London to go back up North!

I don't know how the garage tested the TPS to be honest either!

Here is a picture if the Throttle body with TPS located behind the Varioram Kit

G

That is a substancial nightmare / job then if it's engine out to replace a sensor! I'm not sure if this is a switch or a

potentiometer ? if the later and it's faulty this could be a reason why it's not registering to the ecu the correct exact throttle

position and hence your getting a shunt? The switch type on my 1987 Porsche 924 2.7 tells the ecu when it's open or closed only,

no info on 1/4, 1/2, or 3/4 throttle etc..the AFM Flap device does the rest of the calculations dependent on air speed and load etc.

The only other thing I pick up from your descriptions is the 6th gear at 40mph thing which most car's would shunt at such low rpm and a high gear? I have a lightweight crank (knife edged) and a lighter aluminium flywheel and it can be tricky in traffic crawling at low speed (20 mph) often 2nd gear is too high and 1st is required but's then it's too low and the drive gets shunty..

R

 

[chas3.2]

When I fitted a new throttle cable to mine the first butterfly would jam in the body the bracket that rests on the stop screw was bent stop so the butterfly closed to tightly ,I reset it with a 5th feeler blade never found what that setting should be, nearly stoped my jerky lift off, may be it needs more, you can just get to the adjusting screw with the manifold in place top left hand side, to remove the manifold you must remove the throttle cable at the peddle end and lower the engine at the rear. With the manifold off don't drop anything down the inlet holes. I fitted new engine mounts all round, 3 part clutch - duel mase flywheel, striped the drive shafts and checked for were repacked with grease. Still jerky.

Charles

 

[Graham-S]

The TPS is a Potentiometer from what I have been told. Pre Varioram you can get to it but not after as no room. It's tight doing the Idle Control Valve at the top

The TPS is on the left of the top Throttle valve (Black Unit) Linked via a shaft from the flap

I need to ask the Garage what they did to test it whilst the engine was out!

I know 6th gear at 40mph is pushing it but it does it in 2nd and 3rd etc too. 1st or 2nd in traffic make you look like a kangaroo/muppet!

G

 

[Graham-S]

Charles

How long have you had this issue? So we have both done clutch and DMF now which hasn't fixed the issue!

Yours bad trying to crawl in traffic too?

Can't picture where the adjustment screw is as the Car is back at the Garage having other issues that arose from work done last year by the dealer!

Graham