77 911: throttle stuck open, linkage operates as intended

[blackrado]

Prologue: i have searched quite a bit and found lots on sticking throttle, but all of those have to do with the actual pedal cluster/box and such malfunctioning. This is a rebuilt pedal cluster that still operates as intended. Thanks.

Hi all, i just got home after having my 77 911 inspected (PASSED!!!). I went to take it out for a ride and, im told "due to a leaky injector", i sometimes need to depress the throttle to the floor to get it fired up when warm. This seemed to work fine the last few times i took it out. But now that it was road-ready, of course it isnt working.

I pressed the accelerator down and it didnt fire immediately, so i pushed a little harder. I heard/felt a "click" in the throttle pedal as if i had pushed PAST something. The pedal seemed to return fine though and i have confirmed that the linkage at the throttlebody is operating and returning as well.

Now that it was cold, i went back out, hit the key and it fired up as it usually does, without any throttle input... except it went o the moon! I turned it off well before reaching the limiter. I thought maybe it was extra gas in line from messing with the pedla, but it has now done this about 5 times over the course of 24 hours.

The car has a newly rebuilt 1980 3.0, high compression, small port, with CIS and M1 cams. Could it be that its something in the CIS that i "pushed through" due to maybe a misaligned or poorly adjusted component in the linkage?

Any insight is helpful.

[911obgyn]

Linkage in the tunnel may be interfering with clutch cable. Up by the gas pedal

[Otter74]

I agree it seems most likely that it's a problem with the tunnel linkage. If it's not catching on the clevis for the clutch cable, it could be sticking as it moves sideways in the guides due to worn or altogether gone bushings inside the tunnel. One bushing is visible from the door for the shift coupler, one is under the handbrake and one is just ahead of the shifter.

[blackrado]

thanks! well i figured it out. The pivot arm from the bracket attached to the gas pedal bent to the right and was catching on the stamped/unibody section of the tunnel. I bent it back and all was well. drove it for a piece and before i knew it i had the same problem. After limping it back home and adjusting one last time, i noticed there is now significant travel without actual linkage movement. Seems i may have a bend somewhere in the linkage causing a "springing effect" and likely need the bushings you all mentioned.

[David Inc.]

When you say significant travel, travel of what, the pedal? And which linkage isn't moving with pedal travel? Does the pedal come all the way up on its own or can you lift it without it popping off the arm down to the pedal cluster?

When I redid my bushings in the tunnel the only symptom was rattling, and they had completely failed. I can't see something in there causing the linkage to stick the throttle open.

I would check as well freedom of movement at the bell crank off the side of the transmission and the linkage plate on top of the engine.

[Trackrash]

Originally Posted by blackrado

thanks! well i figured it out. The pivot arm from the bracket attached to the gas pedal bent to the right and was catching on the stamped/unibody section of the tunnel. I bent it back and all was well. drove it for a piece and before i knew it i had the same problem. After limping it back home and adjusting one last time, i noticed there is now significant travel without actual linkage movement. Seems i may have a bend somewhere in the linkage causing a "springing effect" and likely need the bushings you all mentioned.

"Rebuilt" pedal assembly? Was the bushing in the pivot arm replaced with bronze? It sounds just like that bushing is loose.

Reason why I ask is some of the bushing kits don't include that small bushing.

[Rodsrsr]

Originally Posted by blackrado

thanks! well i figured it out. The pivot arm from the bracket attached to the gas pedal bent to the right and was catching on the stamped/unibody section of the tunnel. I bent it back and all was well. drove it for a piece and before i knew it i had the same problem. After limping it back home and adjusting one last time, i noticed there is now significant travel without actual linkage movement. Seems i may have a bend somewhere in the linkage causing a "springing effect" and likely need the bushings you all mentioned.

I've seen this occur several times on these cars. The tolerance is close enough so that it may catch if the arm is bent at all or the bushing is worn.

On my car I bent that section on the tunnel slightly to prevent this. Had it happen to me once in wide open throttle situation....never again.

[snbush67]

Originally Posted by snbush67

Yes, that replacement piece is weak ( I think the original was stronger), it bends and gets stuck under the tunnel opening. Here is a fix that Ian (Icarp) came up with yesterday.




Shaped a piece of steel to fit the contour and created a small lip for the weld to contact on the bottom. No more danger.

^ This mod keeps the piece from bending and a pedal stop is recommended.

[Rodsrsr]

Clever!

[winders]

That’s not a fix. It just moves the problem to another part of the linkage. The solution is to use a pedal stop as the Factory intended. If you have the pedal stop adjusted correctly, this stuff can’t happen.

[Rodsrsr]

Originally Posted by winders

That’s not a fix. It just moves the problem to another part of the linkage. The solution is to use a pedal stop as the Factory intended. If you have the pedal stop adjusted correctly, this stuff can’t happen.

Looking back, that's probably true. But I still like a second layer of protection for piece of mind. I've seen this happen too many times.

[winders]

Except it is not protection at all. All you do with this “fix” is bend something else or put stress on something else that will break. Porsche could have easily made that part much stronger.

[snbush67]

Porsche should have made that part much stronger. Especially with the craptastic plastic pedal stop, a stronger reverse throttle linkage won’t bend.

[blackrado]

Thanks all for the insight. I agree with the strength of the replacement piece.. I can bend it with my hand…no bueno. I will do the bushings because, to clarify, the “play” I’m referencing is when I remove the pedal and just use the rods, I can physically move the pedal mechanism about an inch befor it engages the throttlebody.

I will also bend that but it gets caught on with my “persuader”, install the stop, and likely strengthen the arm itself as Ian did.

Not a fun experience to have to guess whether the throttle will stick and you will need to get creative to get the RPM down.


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