Snapped accelerator cable on 96 manual 993

[D Ward]

Hi

Wondering if anyone can help me with what I am assuming is a very rare problem (as cannot find anything on any forum) whereby my accelerator cable snapped on my 1996 C2 993. Luckily at the time I had only gone a short distance from home so managed to recover back to the house in idle!!

The problem that I now have is that having renewed the throttle cable...not an easy job for anyone with Varioram due to the much larger inlet manifold. I am struggling to get the set up right - and this is where my confusion begins.

I am using the Durametric diagnostic software to connect into the car and read the 'actual values' off on my laptop.

The 993 manual says that the throttle cable should be adjusted so that when you read the 'actual values' on the diagnostics it is at 0 degrees when throttle closed/idle and at 83 degrees when throttle fully open - unfortunately there is nowhere near that adjustment available and the maximum I have been able to achieve is 70 degrees...and that is with the pedal disconnected and the rod pushed as far as it will go.

The wide open throttle position sensor (actual values menu) is kicking in at approx 66 degrees but I just cannot get past 70 degrees.

Double checked that I have the correct throttle cable for the car (as there are approx 16 different variants available) and it is correct for year and model.

I then checked my brother's Porsche 993 C2 carrera 1997 model and found to my confusion that the fully open throttle position is 44 degrees (ie pedal to the floor). As far as we are aware the throttle has never been changed on this car as it has only doe 33,000 miles and had 2 owners...so would have to assume it is set up correctly?? His is also the same in that the wide open throttle detection does not change in 'actual values' menu as it does not go past 66 degrees.

The only thing that I can think is that the 83 degrees listed in the 993 repair manual is for the tiptronic models - and that the manual version requires a different setting? Does the wide open throttle detection play any part with the manual models...or is it only a feature required for the tiptronics - as they also have a kickdown switch for hard acceleration??

If anyone knows the answer to this - or has a manual C2 993 with varioram and has the appropriate software to check these actual values then I would really appreciate a comparison...as I am totally baffled by this.

Heres hoping that someone will be able to enlighten me. []

Many thanks

 

[D Ward]

Hi everyone

Just some additional information regarding this problem - I have enlisted the help of my brother to actuate the two butterfly valves that sit on the throttle body housing (behind the varioram inlet manifold - next to the MAF meter housing)

When you open the top butterfly fully - the 'actual value' in the Durametric diagnostics screen reads 44 degrees.

If you then push it further it goes to 87 degrees 'actual value' and the second 'lower' butterfly valve opens. This would seem to support the information that is in the 993 manual (which only mentions the throttle angle fully open at 84 degrees in the 'automatic transmission' section - there is nothing in the manual transmission section)

Now the question is ' do the manual transmission 993's not use this lower butterfly valve - as the full throttle position I can obtain (44 degress) seems to only open the top butterfly valve'?

This would seem that you are not getting the full benefit of the engine as you are only getting 1/2 the airflow at full throttle.

I hope that makes sense to everyone - and I am really hoping that someone might be able to shed some light on this.

Many thanks

 

[dommorton]

Wow that sounds bizarre!?

I can't image Porsche having a second butterfly just sat unused on manual cars. They would surely use a different throttle body if it's really necessary for tips?

 

[D Ward]

Well there are two different holes on the engine bulkhead for the throttle cable to go through - hole A if you have a tiptronic and hole B if you have a manual transmission. The throttle body also has 2 different mountings for the throttle cable depending on transmission. So I could potentially see how there might be two different settings on the same assembly depending on which transmission type you have.

Someone suggested that I rig a piece of wire up connected to the second butterfly in order to see if it makes any difference by opening the second butterfly whilst I'm drivng along....but I'm not sure that I would be happy to do so whilst not knowing what the repurcussions might be if it is not designed to work that way. Plus a piece of wire hanging out the window at speed as a secondary throttle cable does not seem the safest idea.

Any further info on the correct fully open throttle angle for manual transmissions, and whether the 2nd butterfly valve on the throttle housing is utilised would be greatly appreciated.

 

[Mark Elder]

Well, that was a good excuse to get the Durametric software onto my new laptop (that's about a year old - so I've obviously not been playing with my car's diagnositics for a while).

Bad news is I have a couple of faults on the heater system (which I suspected because the screen is not clearly as quick on the driver's side as the pass side).

Anyway: Results for my throttle are:
Closed 0
Naturally fully open 77
Really pressing my toe down (!) 80 (must press harder in future)

"Throttle Fully Open" switches between 65 and 66

So, I'm now wondering if there is more power to be had....[]

 

[D Ward]

Damn - that means I am well down on power - second butterfly isn't even opening and max throttle position is 45 degrees!![]

Wide open throttle positiion isn't activating and quite clearly there is lots more power to be had!!

Can you just confirm for me that you have a manual transmission varioram engine?

The manual says that fully open throttle position should read 84 degrees +/- 3 degrees - so theoretically you have another 3 degrees of throttle actuation.

Anyone else got any further info on this problem and also maybe some thoughts on the throttle cable routing? Perhaps that is where the problem lies - although I hope not as it is a right royal pain in the backside to change the throttle cable.

 

[D Ward]

Hi Maurice

Many thanks for the reply - I understand what you are saying about the Varioram system - whereby the inlet tract is altered by the use of vacuum operated actuators located over the inlet tract to change the performance of the engine at a set rpm range thereby increasing torque and power in that range. Unfortunately the problem I am experiencing does not relate to this part of the system - and I checked all the varioram actuators were holding vacuum when I had the inlet manifold out to change the throttle cable.

However, there is a double butterfly valve on the throttle and the top section opens up between 0 - 45 degrees, as far as I can make out the lower portion of the butterfly is then actuated through the final range from 45 - 84 degrees. You cannot see the throttle assembly on the varioram unless you have a boroscope or a mirror as it sits bolted centrally on the inlet manifold right at the back of the engine bay. So the whole spider,ICV and MAF sensor block any view when looking with the mark 1 eyeball. If you look at the right hand side behind the the ICV and to the left ot the MAF sensor you can just see the electrical plug for the throttle potentiometer/position sensor.

The part number for the throttle assembly is 993 110 125 06 and if you type that into the search function on the PET catalogue for the 993 it will bring up a picture of the assembly which clearly shows the two butterlfy valves - one at the top and one at the bottom

From what Mark was saying it would clearly seem that I am not getting the full range of throttle movement - and therefore the lower butterly on this throttle assembly is not opening...unless I manually operate it further than the throttle pedal will travel..in which case I can get both open and the full 84 degrees of throttle position.

I currently have the car back on the road as it is near MOT time and I will investigate further once that is out the way - probably put the cat bypass pipes on at the same time as anything involving the throttle cable being moved/refitted at the engine pretty much involves removing the whole inlet manifold (on a varioram) - unless you are a gynaecologist with arms like pipe cleaners!!

So any further info anyone has on the throttle cable positioning would be greatly appreciated - I have tried adjusting the turnbuckle on the cable to increase the range of throttle angle available - but there is insufficient adjustment to achieve the range quoted in the manual.

Incidentally I found out today that my brothers Porsche had it's engine removed at approx 20,000 miles and his has the same range of movement as mine (0 - 44 degrees) - so perhaps something is being overlooked on refit / routed differently that is causing the problem. I must say the Porsche 993 manual is very sketchy about the accelerator cable/throttle housing. Perhaps someone has removed their engine at some point and could confirm where the cable is supposed to locate/route.

Cheers for the replies so far - at least I know that someone is acheiving full throttle position even if it's not me! [&o]

 

[Mark Elder]

ORIGINAL: D Ward

Can you just confirm for me that you have a manual transmission varioram engine?

Hi Darren,
Yes it's a 96 manual varioram coupe (although it is a C4 - so not exactly same as yours).

What I don't understand in this is how cable routing can impact how much it pulls the throttle open, unless the pedal does not have the original range of movement (has someone fitted some form of stop in the past?), or unless there is some gear / pully type mechanism at either end which is missing. But you have the PET so I guess you would have spotted if something was different.

Have either yours or your brother's cars been on a dyno? Would be interesting to know if they are actually down on power...

 

[D Ward]

Hi Mark

Thanks for letting me know that yours is essentialy the same engine wise, etc..

The only other think I can think of is that the throttle cable supplied was not correct in the bag, so although the part number on the packaging is correct the contents were not.

The cable sheathing outer length could be changed slightly by the routing - ie. increasing the bend radius which would have some affect on the throttle movement.

I previously wound out the adjuster barrel that enters into the cable tunnel taking the accelerator up to the foot well area and this increased the throttle angle to 60 degrees from 44 degrees.

The pedal board appears to be the original fitted and the stop plate on there is fixed with no adjustment.

Does make you wonder how may other peoples 993's might be in the same situation and not even aware of it. The car is still quick, but doesn't feel like it is achieving it's full potential.

Further investigation definitely required when I have some more spare time - car has just passed MOT so will look to do it when I fit the bypass pipes and change one of my mufflers. As you definitely require good access from underneath the car - so if I'm going to remove the majority of the undertrays I might as well kill two birds with one stone - engine and gearbox oil might also be in order while I'm feeling enthusiastic.

Cheers

 

[Guards Red]

Hi,

The correct cable should have a curved metal sleeve at the end where it goes through the engine tin to the throttle butterfly. The none Varioram engine does not have this. Having said that, both cables should work. Are you sure you have the cable going through the correct brackets on the manifold?

The second butterfly is mechanically linked to the first via a cam and lever system. As long as the throttle arm is being pulled all the way by the cable the second butterfly will open. The easiest way to check this is mechanically. Take off the airbox and MAF. With both off you should be able to put your fingers in the throttle housing and feel both the butterflies. Takes a little practice, but you should be able to do this. I can and I'm stumpy. Get someone to carefully work the throttle pedal whilst you check how it opens. You can feel both butterflies and push on them either way to ensure they are fully open.

With the engine blower removed you can also feel the throttle levers (from the left side of the engine as you look at it) and check they are fully open. With someone pressing the pedal fully you can just get your arm on the levers and push them against the throttle stop. If the lever moves a little with the pedal all the way down you do not have VOT (wide open throttle). Equally you have to check with the pedal fully released it closes entirely. Much easier than relying on the switch.

Hope the above helps, let me know if you need anything further.

Regards
GR

 

[D Ward]

Evening

Many thanks for the post - the throttle cable does indeed have the curved metal sleeve that passes through the engine tin to the throttle butterfly - the rubber grommet is also engaged in the mounting to the side of the throttle assembly.

I can actuate both the top and the bottom butterfly by mechanically actuating the throttle assembly - the problem that I am experiencing is that I cannot achieve this with the accelerator pedal. There is insufficient movement/travel or rather transfer of the pedal application to allow full actuation of both butterfly mechanisms.

If I manually operate the thottle assembly at the body I can get the full range of movement/angle - from 0 - 84 degrees and the durametric software confirms this as well as wide open throttle position going 'high' at approx 66 degrees.

The problem that I am experiencing is that I am unable to acheive this range 0 - 84 with the pedal. I currently have it set at 45 degrees (pedal to the floor) - and even if I wind the threaded rod in at the end of the throttle cable (which secures it to the ball joint), adjust the pedal rod to it's fullest extent to increase the pedal travel range and wind out the cable outer sheath adjuster (where it enters the throttle cable tube to the drivers footwell) under the car in the transmission tunnel to it's full extent to effectively lengthen the outer sheath.... I can still only achieve 61 degrees.

I have to confess that I am slightly baffled by it all and I appreciate your response because it kind of confirms the info I had gleaned already.

Do you by any chance know how the throttle cable should be routed under the car from where it enters/exits the underbody to drivers footwell tube back to the engine tin where it goes through into the engine bay. If we strectched the outer sheath out (increased the bend radius by hand) we could achieve 78 degrees - hence why I wondered if the routing was incorrect.

Thanks to all those who have provided info already -it is greatly appreciated!! []

 

[Guards Red]

Hi,

Must admit to being somewhat baffled myself. I've replaced the throttle cable but some years ago. I doubt the routing could be wrong as its pretty hard to get wrong. As you say most of the cable runs in a metal tube in the transmission tunnel. From there the outer sheath and adjuster take the cable to the engine tin and directly to the throttle lever. I think you probably have this right but as you know the throttle body has two separate runs, one for automatic transmission and one for manual. Each run has a cable stop and an attachment for the cable to the throttle actuation lever. In there is an attachment point for cruise control too. It is possible to get the runs crossed up with the cable stop for the auto running to the lever for the manual. (Not sure if that makes any sense at all, my apologies if it doesn't). I'd check these first.

Taking the Durametric out of the equation, can you get full throttle with the pedal checked with your fingers? If so, perhaps the throttle position sensor is at fault? If not, the only other thing left to adjust is the pedal rod. With the pedal disconnected from it's ball joint you can lengthen or shorten the rod which may prevent the throttle pedal hitting it's stop before the throttle has fully opened.

Hope you get it sorted.

Regards
GR

 

[D Ward]

Hi

Thanks ever so much for that reply - what you have said about the cable stop does make sense.

I have gone through the correct hole at the engine tray for the manual transmission (hole B) or the right-hand one when viewed from the rear of the car looking forward.

However, I did not realise that there were two cable stops on the throttle body (when you say cable stops I'm assuming you mean the rubber grommet that the outer cable sleeve/sheath would push against) - at the time when I fitted it I was reached round the back of the air intake due to the fact that I had already fed the throttle cable through.

If there are two of these (one for the auto and one for the manual throttle cable then I can see how the reduced range of travel could be caused)

You took a picture of the throttle housing and placed it as an attachment - do you think that you might be able to take a close up so I can see the two?

If it helps my throttle cable grommet is fitted to what would be the left hand position of the throttle body housing (when viewed from the rear of the car looking forwards) and then runs up into the manual position on the throttle (which I believe is the right-hand section that has a small cut-out to allow the cable to slot in and then pull down into position)

To be perfectly honest with you I just fitted it the way that the original cable had come out - so quite clearly it had been an issue in the past...I just never realised until the cable snapped and I went through the set-up process.

If I hadn't had the Durametric software I would quite possibly never have known.

I think that if as you say there are two of these grommet mounting points on the throttle assembly then you may just have cracked it!! I will try and get round to checking next week and post back accordingly!

If you have any further info please do let me know...many thanks GR you are a star![]

 

[Guards Red]

Morning,

Feel a bit of a k**b now as Having dug up some photos I'm not sure I've given to the right info. Hole "B" is right for a manual Varioram but I remembered there being two outer sheath stops but there's only one. There are two attachment points for the lever however. The correct one is the upper, nearest the throttle body. The outer one will not allow sufficient travel and is for the cruise control. See these pics:

http://i823.photobucket.com/albums/zz153/guardsred/DSCN1697.jpg

http://i823.photobucket.com/albums/zz153/guardsred/MyVarioramParts005.jpg

http://i823.photobucket.com/albums/zz153/guardsred/MyVarioramParts017.jpg

 

[D Ward]

Hi GR

Thanks for the reply - and the photos.

Feeling slightly deflated now as quite clearly from the pictures I have it routed through the correct assemblies on the throttle body!!

So it is configured correctly for the manual transmission - totally baffled now...beginning to wonder if I really do have the wrong throttle cable. Double checked the bag that the cable came in and there are three stickers all confirming the part number - and I also confirmed with the parts department using the chassis number.

My only other thought is that the wrong cable has been 'picked' at the central distribution hub in Swindon and so although the part number is right - the part contained in the bag is wrong? Not sure if there is a part number printed on the sheath or cable assembly anywhere to confirm this.

My brother is gloating now as his is quite clearly mounted in the lower 'cruise control' point - which explains his lack of throttle travel. So he is understandably quite chuffed about this...be interesting to see what difference it makes as a direct comparison between cars when he has fitted his correctly.

Still doesn't help me though - totally confused and thinking I'm going to have to remove the entire inlet manifold again this weekend [&o] - really need to get to the bottom of this mystery!

Any further info greatly appreciated before I remove the entire upper engine bay!!

Big thanks for all the info posted so far.

 

[Guards Red]

Hi,

At this stage if you are confident that the cable is attached properly at the throttle end there is little to be gained from taking it off again. Besides it's a pain in the butt.

As far as I'm aware the part number you should have is: 993 423 024 82 (RHD, Manual). Left hand drive, RS, Turbo, non Varioram are all different. Thing is as long as it fits, ie gets from the ball joint at the pedals to the lever it should work. The only reason it wouldn't is that the outer sheath is loose in it's mountings. this will mean that some of the pedal movement will be taken up just clamping the sheath. This can only happen under the car, the bit between the solid tube and the sheath stop on the throttle body. Did you remove the metal transmission tunnel cover? Again from memory I had to do this to ensure the sheath was seated properly. If I had to guess this is where I reckon you problem is.

So, first step jack up the back of the car and remove the metal trans cover. You need to be careful as the bolts welded to the body love to shear off. With this off you can trace the cable right through from the pedal to the engine. The problems I had fitting the cable were all at this junction, you have to fully push the sheath home into the metal tube.

Let us know how you get on.

Regards
GR

 

[D Ward]

Hi GR

Part number is correct - this is what I was supplied with and what it says on all the packaging (not sure if it is stamped anywhere on the cable run??)

You're right about the transmission tunnel it had to be removed to access the throttle tube that the cable slides into - there is then a plastic sleeve (that slots onto the under body to drivers footwell tube) with a hex head and female threaded portion - there is then a hex headed male threaded portion that screws into this. The throttle sleeve then runs back from here and over the gearbox linkage (there is a large round rubber buffer around the sheath that sits on top of the linkage to stop it rubbing (I assume this is the case as this is how the old cable ran)

It then runs up to the side of the transmission and there is a plastic securing clip that holds the run and stops it flapping about - it then goes further and extends through the appropriate hole (B for manual transmission) in the engine bay tin before going to the lower grommet mounting point on the throttle body and then up to the thottle actuation linkage (the right-hand higher one viewed from the rear of the car)

Now the only other thing I wanted to ask was whether there was any sort of grommet or fixing that went in the hole (A or B - depending on transmission) in the engine tin (where it passes through from the underside of the car to the engine bay) ?

The only other thing I can think of is that I have bolted the grommet mounting bracket on the wrong way up on the throttle housing - as I seem to remember that I had to remove it to get the grommet into position - I wonder if this could have an affect as it may have change the tension imposed on the cable sheath.

Let me know if you can confirm any of these things particularly the bit about where it passes through from the underbody to the engine bay.

Thanks for all your help so far - and to all those that have contributed...nice to know there is a support network when things go wrong.

 

[Guards Red]

Hi,

That all sounds fine to me. Don't think the cable has any numbers on it but I'm not sure.

I guess you could remove the blower fan and check the mounting of the sheath stop with a mirror against the earlier pictures? Have you checked the butterflies manually or are you relying on the Durametric?

I remember the Durametric does not show 100% ever, I'd check again but I'm now on a Mac which will not run Durametric's software.

I feel your frustration, keep at it I'm sure you'll figure it out!

Regards
GR

 

[Guards Red]

Copied this from a fellow on Rennlist:

"You should be able to get WOT when the pedal is floored. If you don't then the cable is too short i.e. the outside lining of the cable is too long. Use the adjustment to shorten the outside sheathing as compared to the inner cable...that changes the relative position of the inner metal cable to the sheathing and effectively changes the cable length".

Couple of pics with the cable end engaged and disengaged:

http://i823.photobucket.com/albums/zz153/guardsred/engine_removal_throttle_cable.jpg

http://i823.photobucket.com/albums/zz153/guardsred/throttle_cable.jpg

Hope they help

 

[D Ward]

Hi GR

I'm just going through the manual and the PET at the moment - trying desperately to find anything that might shed some light on things.

Operated the butterflys manually by managing to get fingers round - with the throttle assembly fully depressed (at the engine) both butterflys are opening (you can feel it) and the Durametric software reads 84 degrees (or fully open) which is correct.

If I depress the accelerator you can feel the top butterfly opening and the durametric shows 44 degrees - I can then put my hand round and push it further to the fully open position and 84 degrees again shows on the durametric.

I know there is some confusion regarding the throttle - it will never show 100 percent on the durametric - fully open is 84 (degrees) and this is indeed the Porsche specification (+/- 3 degrees) for the throttle.

What I did see in the manual is that with reference to the two holes that come through into the engine bay (A - Tiptronic / B- Manual) that there is what look like a spring clip with a plastic clip in the centre of it (this gets reference C) and it appears that this is supposed to clip into the engine bay tin in either A or B hole.

Now I have not got this - and indeed it was never present when I removed the old throttle cable - it makes me wonder if this item secures the cable and prevents any flexing of the sheath that would dampen out your throttle pedal actuation?

Does yours/did yours have this item fitted - if so this could be the thing I'm missing - but I cannot find any reference to it for love nor money in the PET catalogue.

I think my eyes are going square from looking at a computer screen excessively!!

Cheers