Sticking throttle, high idle

[Irhmsd]

OK, so I brought the 1974 911 with the 3.2 home today after 6 months of restoration. It looks stunning and runs amazing. One issue. When I get to traffic lights, it wants to idle at 1400 - 1600. Obviously too high. So, I can fix this by gently lifting up the accelerator pedal. It will pull up about 1/16 to 1/8 of and inch and the idle drops right down to a smooth 500, even when I release the pedal. However, once I drive to the next light, the idle is high again until I lift the accelerator pedal ever so slightly. Somewhere, something is binding just a little when I let my foot off the gas. What should I do?

Ivan

[kidrock]

Check your linkage where it connects at the transaxle bell housing. Clean and lube as necessary.

[sf911]

Check the secondary return spring , it attaches to the under side of the left side of the intake manifold on a 3.2

[steely]

Originally Posted by sf911

Check the secondary return spring , it attaches to the under side of the left side of the intake manifold on a 3.2

There should actually be 2 springs here, one on either side of the bellcrank.
You can check the bushings too on both bellcranks (on engine deck and transmission), and the spring and linkage on the throttle body itself.

Ivan, I'm in Horsham if you ever need another one to compare with.

[Irhmsd]

Thx guys. Sounds like all this stuff requires a lift. May need the dealer. Lol

[tdw28210]

Check the bushing in the pedal cluster.where the base of the pedal connects. They go bad and can result In high idle or worse.

[Irhmsd]

Cluster was completely rebuilt, bushings and all.

[DRACO A5OG]

Here you go:

THE FIX: Binding Accelerator, NOT Pedal or Bell Housing BUSHINGS, not even @ Tunnel

Also check that the idle switch is engaging properly, sound like it is not resting enough to fully engage the idle switch.

[198491132]

Originally Posted by DRACO A5OG

Here you go:

THE FIX: Binding Accelerator, NOT Pedal or Bell Housing BUSHINGS, not even @ Tunnel

Also check that the idle switch is engaging properly, sound like it is not resting enough to fully engage the idle switch.

+1....idle switch test

[JDC911]

Originally Posted by Irhmsd

Cluster was completely rebuilt, bushings and all.

I had the same problem and I rebuilt the cluster and almost wrecked or blew the engine on my 85 911 on the test drive . I just kept tapping the gas without touching the clutch and it stopped being stuck. I took another look at this problem and found that the linkage on the back of the gas pedal was getting caught on the body directly behind the gas pedal . I used a mini grinder (Dremel) and cleared the area of the factory obstruction in the design. It works great now. I have learned so much from the forum that I really wanted to share this. These cars are great but there is always room for improvement. I believe that being a pan construction type car, that over years of use has made the bottom of the car rise (by either jacking/lifting up the car or hitting something) in this area of the gas pedal and there was no room for this in the original design.

[JDC911]

Originally Posted by Irhmsd

Thx guys. Sounds like all this stuff requires a lift. May need the dealer. Lol

Not the dealer, most know almost nothing about the air-cooled cars. You can buy a car lift and all the tools for what they will charge you. I had a Porsche dealer tell me that I had a rod knock and I bought a engine stethoscope ($50.00) and found the real problem. It would have cost $12,000+ to have them rebuild the engine and found that it was a loose timing chain and the tensioner was hitting the timing cover/case. I used the forums for information and bought all tools,parts needed including a lift for less than $3000.00 .I did the work myself and now my car runs great.

[fanaudical]

Does your '74 still have the hand throttle installed? The reason I ask is that sometimes you can get some "stickiness" in the throttle rod bushings that run through the tunnel near the hand throttle lever. Also, the plastic block (on the bottom of the hand throttle lever) that moves the rod can "grab" the throttle rod if the rod is dirty, has old grease, or the block is starting to disintegrate from age.

[mikael_s]

Sorry can't help with the problem but would love to see pics of the car! 74 Targa with 3.2 = fun!

Originally Posted by Irhmsd

OK, so I brought the 1974 911 with the 3.2 home today after 6 months of restoration. It looks stunning and runs amazing. One issue. When I get to traffic lights, it wants to idle at 1400 - 1600. Obviously too high. So, I can fix this by gently lifting up the accelerator pedal. It will pull up about 1/16 to 1/8 of and inch and the idle drops right down to a smooth 500, even when I release the pedal. However, once I drive to the next light, the idle is high again until I lift the accelerator pedal ever so slightly. Somewhere, something is binding just a little when I let my foot off the gas. What should I do?

Ivan

[privatepang]

Reviving an old thread as I have the same issue. Ie lift the accelerator to get idle back to normal. Doesnt happen all the time. I have running a 3.5 twin plug with motec. Not mechanically minded but tried troubleshooting based on research. Cant find the idle switch .

There doesnt seem to be a secondary return spring on the bell crank in the engine bay like ive seen on other cars... i assume there isnt a spring on the bell crank on the transmission. Bushings seem fine there.

If I pull the throttle from within the engine bay, it completely pushes back. If i do the same thing from the accelerator pedal , there's it doesnt spring back to 100%

My next step is to look at the pedal cluster but i assume the pedal cluster has to come out to change out the bushings connected to the throttle pedal right? I've read that its a pain to reinstall...

Few pics for reference.

[EC900]

A little lubrication on the engine area joints will help. The t-rod at the trans can be disconnected to check the condition of the nylon bushings on the b-crank, they look new but my be out of round.

As far as the pedal cluster bushings very likely the source of the hang up…it’s not as difficult task as seems, but much easier if you remove the seat.
If the pedal cluster is the same as Mid Years, the bushings (2) can be replaced simply pull a small cotter pin and linkage can be put aside, no major dismantling.

Good lighting, steady hands, magnetic pick tool because the pin might drop out or go missing, maybe reading glasses to find the hole for the cotter pin and no seat seat in the way. New bushings can be oem nylon or bronze, I used nylon at the time because bronze were no in stock, lube nylon bushes with light coat of silicone paste for good measure.

There are 3 nylon bushings for cable in the tunnel along driver side held in place by bendable tabs, they can contribute to sticking as without them it may cause rod and cable to hang up. A console, shifter and handbrake all need to be removed. You can see with an inspection mirror thru the front and rear tunnel inspection holes if these bushings (at least 2) are disintegrated and broken before going through the process.

[Otter74]

If paying attention to the linkage at the engine doesn’t change the condition, take a mirror and look inside the tunnel by the pedal box, or pull the handbrake up and look in through there - the throttle rod can get hung up on the clutch clevis, or move in ways it shouldn’t because of bad or dislocated bushings in the tunnel. There’s one in the front, one in the middle and one in the rear.

[EC900]

Here’s a link from FCP Euro on pedal cluster rebuilding, and one of their photos I edited explaining what I found to be my culprit of sticking throttle.
Extra credit: check the vacuum hose for the brake booster while you’re there, mine was cracked at bend near the clamp.

https://www.*******.com/blog/how-to-rebuild-the-pedal-cluster-on-an-air-cooled-porsche-911

[privatepang]

Ok thanks all

@EC900 i assume you had to take the whole clister out to rectify the 3 pieces ?

[EC900]

Originally Posted by privatepang

Ok thanks all

@EC900 i assume you had to take the whole clister out to rectify the 3 pieces ?

Not at all. Removed the seat so I could get in the tight spot, pulled the cotter pin and the bell crank shaft will slide out of the way. I think I popped off the gas pedal rod to get it out of the way, so new bushings can slide in each end.

Spent more time taking out the seat.

[privatepang]

Awesome thanks!