2g throttle sticks - not cables

[rhodes2010]

Before posting I searched and read all I could about sticking throttle ,
cables, ISC , TPS, - hate having to post this but I must be missing something.

2G turbo with cruise control - stock under the hood.

1. Lubed throttle and cruise cables - they are now very smooth.
2. Disconnected the cruise control cable to firewall to test.
3. Just took off elbow and am inspecting the throttle body.
It seems smooth, super easy to rotate and return spring feels good.

Cold or warm, step on gas and go to shift and engine stays at high revs sometimes.
We usually quickly step down on the pedal and let go , letting it
snap closed and the high idle stops.

To me these are classic signs of something binding or stuck.
But my inspection under the hood has turned up nothing obvious.

Looked for deposits around the throttle plate and can find none , a little black
grease like build up, not severe. Mostly at the top inside.

Did find that one of the small vacuum lines (the closest to the firewall of the three lines at top)
has the smallest hole in it, a tear. I will replace this line.

I wanted to pull the entire throttle plate assembly out but found that a coolant line
is connected, so unless I really need to take this out to fix it will work on it
in the car.

Today for the first time I was able to go under hood while it was stuck at
high revs to observe what was happening. All I can say is that the throttle
was rotated like someone was still stepping on the gas like it was stuck.
I grabbed the throttle and rotated it by hand to close.

Clean throttle plate, good throttle spring , no binding, smooth lubricated cables.
Why is this sticking open ?

Hate to purchase a $97 TPS just to experiment.

 

['97 Cayenne]

I know you said your read about the tps ans isc but did you end up testing those for proper ohms/voltages?

Also, did you try unplugging the cruise control plug under the hood? Might be something up with the cruise box, or wiring for that.

If you could, swap in a non-cruise cable. See what that does

 

[rhodes2010]

I just went and attempted to get OHM readings on pins for the 6 ISC
pins and 4 TPS pins.

I have 3 meters, one with a needle that only has 1K ohm setting and two digital
meters with a setting for 20K that I used.

The readings virtually make no sense. I am not confident they are correct.
According to other posts I should get 32-33 ohms on the 1-2, 3-4, 5-6
on the ISC ( I hope I quoted that right). And I was able to get a
35 reading , the rest were all showing a lot of resistance.
I am going to get out my larger needle type and do it again.

So I test drove it and it went into high RPM's again, only once on a 15 minute drive.
And under the hood, this time, I went to the throttle and it was stuck hard.
With some force I was able to close it, like something was stuck blocking the plate.

I unplugged the TPS , just to see what would happen, and nothing happened.
Was even able to rev engine with TPS disconnected.

Wish I understood it all.

 

['97 Cayenne]

Being that you found that it was stuck hard when it happened again, I wouldn't lean towards it being an electrical or vacuum issue. I would assume it being a mechanical issue.

If it were me I would take out the entire cruise control assembly and inspect it.

Also, I don't see how it could happen but the nuts on either side of the throttle body shaft may have loosened and the plate is off center causing it to catch the walls of the throttle body.

I would alsosuggest looking under your dash and anywhere in the engine bay where the gas pedal might be getting caught on something?

Lastly, it's not unheard of for the throttle cable shielding to melt around the cable and cause it to stick.

 

[NHerron]

The spec for the ORIGINAL ISC 'brown top' is 28-32 ohms but if the original ISC was replaced with a new OEM part, it will have a different spec of 40 ohms. This motor is identified by a 'black top'. Here's a link that explains more. And a video from youtube

DSM ISC Motor FAQS

DSM ISC motor testing & Replacement - YouTube


Which is it, you said the plate was physically sticking open or do you just have a high idle?

 

[rhodes2010]

Well, that helps in that it must not be common for a TPS to cause this or something super simple.

Now I can go after the less common. I checked the throttle plate, and it seemed
good, but now I will drain the coolant, pull off the whole mechanism,
will also go ahead and remove all the cable assemblies for close inspection.

Will focus on something mechanical.

 

[rhodes2010]

New information - when I said not the cable I was wrong.

In the cabin , where the cable comes in to the car at top of pedal.

There is a plastic tube or sleeve over the cable, inches long.
When you press down on throttle the plastic tube follows the cable
out of the firewall.

When we let go of throttle the plastic tube hits the outer housing of throttle
tube and stops pedal.

Was able to do this in my driveway with engine not running.

For now I shoved the small plastic tube deep in to the outer cable housing.
If it does not stay there I might try some adhesive (like silicone) to
get it to stay inside outer housing.
The other option is to remove the little plastic tube.

I have never had a throttle cable completely out of car to understand what this little piece is for.

Anyone want to comment on their experience with this small plastic tube
on the throttle cable ?

 

[stiggity99]

rhodes..
nice that you figured it out, when the first clown attempted a complete top end rebuild (labor), he pinched my cruise cable, and that was causing the throttle to not stick, but act-up... ill have to look for a plastic tube on mine ,

--Steve