E-gas accelerator pedal service
 

Hi folks,

I completed a successful project on my 2001 Boxster haven't seen documented that I wanted to share: how to remove, clean, and lubricate the e-gas potentiometer. This may also be called a throttle position sensor. It has a fairly stiff spring in it that internally rub against its housing and this is what causes the "stiction."

The symptom of the service being needed is the accelerator pedal has 'stiction", or a "notchy" feel where it will not move as smoothly as expected. This may be worse at some times than others (in my case, it seemed temperature can have an effect). It can impede driving enjoyment and make smoothly launching the car using the clutch difficult, and is especially noticeable when crusing and making minor accelerator pedal adjustments (because you'll find the pedal won't quite adjust as you'd like).

You can first try disassembling and cleaning the accelerator pedal assembly, which is well-documented online. (For example, on these two renlist threads):
Edit: Exactly how should the gas pedal (BE REMOVED?!) feel? - Rennlist Discussion Forums
Sticky Accelerator on CPO 996 - Page 2 - Rennlist Discussion Forums

However, after tearing into the gas pedal, if you find there is stiction coming from the potentiometer above, this DIY is for you. The accelerator pedal connection to the e-gas potentiometer by a short length of cabling. If you pull on the cable end to actuate the e-gas potentiometer, and notice it making noise or not moving smoothly, service on the potentiometer is warranted.

The potentiometer is mounted to the brake pedal bracket by 3 10mm nuts and studs. Accessing them is bit of a contortionist exercise. The less limber mechanics may find it helpful to remove the drivers seat. (Otherwise, at least moving the seat all the way back.) Remove the heater duct going to the driver's side dash vent, and then you can access the three nuts from below, and reaching around from above if necessary. Use an open end and/or box-end 10mm wrench to get to these nuts. You'll want to have the accelerator pedal assembly either removed from the car, or connected to the cabling and "dangling loose". It is not necessary to remove the cabling from the e-gas potentiometer before removing it from the car.

It's not necessary to completely remove the 10mm nuts to remove the e-gas potentiometer. You can just loosen the nuts, and the e-gas potentiometer will slide out toward the back of the car, and can be removed from the car. (The photo shows the e-gas potentiometer, on mounting bracket, at lower right), and split apart accelerator pedal assembly and connecting cabling at left.

Here is another view of the e-gas accelerometer. Mark the position of the throttle bellcrank to the potentiometer shaft and housing/bracket, (using something like a sharpie) since it will have to come off and you'll want to reassemble it with the original index. It comes off with a 10mm nut.

Next, I grabbed the other end of the potentiometer housing with some vice grips and hinged it open. There are three tangs that keeps it shut. You may break one, but it's not a big deal as it's horribly overbuilt. (Designed to be waterproof, apparently, which is overkill under a dashboard.)

Then you'll need to desolder the 6 wires underneath the cover, and remove the e-gas potentiometer wiring harness from the housing. It just pulls out.

Next, there are three tabs you can lever away from the housing's inside surface with a very small, flat screwdriver. Then, push upward on the shaft to press out the spring and potentiometer assembly from the housing. (Be sure to keep track of the orientation of things so you can reassemble in the proper orientation - recommend using a sharpie to mark index of things, or take photos as you go.)

Now, clean all the dirty surfaces that rub against other surfaces, and lubricate them.

I recommend using a plastic-safe grease here, such as silicone or PFPE grease (DuPont Krytox is a brand name of PFPE oil and grease.) There are two coaxial coil springs, which I managed to lubricate without complete assembly. I found one dry part of the inner spring that needed lube in the picture shown. (Basically, you'll want to make it so the springs rotate smoothly and without stiction or noise.)

The shiny, worn area on the outer spring was also making contact and needed lubrication.

A rib in the housing this spring was rubbing against was also noticeably worn (worn spot visible in attached picture). I decided to lightly lubricate the whole outside and inside surfaces and ends of the spring, some accessible areas of the inside spring as well, as well as the whole length of the ribs inside the housing, before reassembling.

Here are the components.

Reassembling was a bit tricky as the spring needed some pretension (about 1/4 turn or so) to be properly installed. There is probably some special tool the factory used. I got it done by holding the housing in a bench vice and using a thin flathead screwdriver to help with the rotational tensioning.

Obviously to complete the job, re-solder the wires, replace the cap, and reinstall the assembly in the car and reinstall the gas pedal assembly in the car also.

You can also clean and lubricate the cable if desired. I recommend cleaning and lubricating the pedal assembly at this point if you haven't done so already, since it's relatively easy and could help. Enjoy a perfectly smooth accelerator pedal!

Marvel at how much easier the car is to launch from a stop, and how much more of a joy it is to drive! :D

-END OF DIY-

This is great! My car has the throttle stiction issue that you described, so I'll be taking on this project now.

Thanks for the excellent pictures and the tutorial.

Jakeru,

Great write-up, thanks! This will be very useful for anyone who has that issue of Sticktion in the pedal.

I have a separate question for you or anyone who has this assy opened and readily accessible.

What is the resistance range of this potentiometer (throttle position sensor)? I am assuming it is a potentiometer (variable resistance) and not a hall effect transducer. The reason for my question is that in my Boxster Ev conversion I need a throttle that puts out 0-5K ohms to control the DC motor controller. If this potentiometer puts out 0-5K ohms my job will become much easier. Otherwise I have to find another way and use a 'potbox'...

Also if someone knows where the wires from this throttle sensor end up exactly in the engine harness/compartment...

Any info anyone can provide will be helpful...

Thanks.

I am having a problem with my 2000 Boxster. I have a P1502 code and the car is in limp mode. I have been told that accelerator parts may be the cause which will require removal of the dash to reach. I suspect the parts you listed in this post may be the culpit.

Did you remove the dash to get ot these parts?
If not , how did you gain access

Thank you.

Bob
PCSBOB

If your Boxster is a (model year) 2000 it should have the 7.2 DME.
Looking in the Bentley service manual under the 7.2 DME DTC codes.
P1502 is for (fault type)= Fuel pump relay output stage. (explanation)=short to B+/above upper limit/rich mixture threshold.
I would start by changing the fuel pump relay.
They are around $10.00 I think.
Do that see if it changes anything.

The issue your chasing is a throttle jacking spring issue??? (or other issue) but that is pre-2000 year models with the 5.2 DME. and non E-gas throttle. If you reference the Bentley service manual you will see P1502 under the 5.2 DME is for a jacking spring issue.
So Porsche used the same P-codes to reference different problems dependent on which DME or ECU the code is tied too.
Hope the Bentley manual is correct and that this helps.

If changing the fuel pump relay has no affect then-
Check the wiring from the DME to the fuel pump relay for a short to Battery positive.

After that if you have a scanner that will show it????
I think you can hook it up step on the throttle and see the % the throttle opens.
That should prove out if your throttle is the problem or not.
Much better then taking things apart if you don't need to.

Maybe I didn't have to just replace my whole pedal assembly then. Great diagnosis and writeup.

I'm a little big and working under the dash of my Boxster seems it would be physical torture, so probably I don't mind having had the Porsche dealer change this for me. It's the only time they've seen my car.

Thanks
 

Jakeru, thanks so much for writing this up. I bought a 2000 996 a week ago and the stiction in the throttle was driving me crazy. I disassembled and lubed the pedal linkage... before putting it back in the car I pulled the cable going to the poteniometer and felt the stiction. Your instructions were spot on, thanks again.

Thank you for sharing this. Would you mind sharing a link to a video if possible. Then What kind of lubricant are you using?


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I'm bumping this thread because it speaks to a problem some people might not even know they have. My throttle was behaving as others described, especially noticeable at low speeds. I got away with just removing and lubricating the pedal assembly, I didn't even take it apart, just sprayed lithium grease in on the mechanism and on the cable. This has transformed launching the car and low speed throttle control.

Good how-to!

On my 2002 986, neither the bracket that the potentiometer bolts to (shown in photos in original posts), nor the bracket that that bracket bolts to, have slotted holes that would mean you can avoid taking the nuts or bolts off fully. I found it much easier to just unbolt the potentiometer from its bracket, which is only 2 nuts, and they are both very easily accessible. You can then easily unhook the cable inner from the cam. If you want to get at that end of the cable, that clips into the bracket, it is also fairly easy to squeeze the tabs and pull that out.

If you have/want to take out the whole assembly, do it by unbolting the main bracket that the bracket that holds the potentiometer bolts to. At first, I thought I was supposed to be unbolting the potentiometer bracket - you’ll get that off, though one nut is a pain, but you will never get it bolted back on again without removing the other bracket, bolting it to that, then bolting the lot back in again.

Oh, and the whole procedure worked and got rid of most of the stiction feel. I’d say it is still not entirely gone at start of pedal travel, but better than before.