Sticky Throttle? (GT4)

The round object you see is a wheel, actually a cam as its offset to be an eccentric. It does exactly what you imagine. When cold it advances the throttle. It would contact the lever to the left of the wheel in your picture, and advance the throttle. In your picture the foot of the lever is NOT contacting the wheel, so if this is the normal case when you are idling high, that part would NOT be your trouble. If it is contacting, the small nut in the center can be loosened and the wheel rotated. Make sure your throttle cable has some slack. If so, maybe you need some more adjusting.

 

Mid engine cars have been known to have the throttle cable's internal sheath get melted from the heat of the headers. Makes for a sticky cable, especially when hot. Could this be an issue on your car?

Ken

 

David,

This is going to sound dumb, but...

I recall reading past threads about sticky throttles, and it being attributed to the floor mats. They shift around, and get caught under the throttle pedal, causing the throttle to "stick".

May not be what's happening here, but at least this would be easy, and cheap to fix if it were the case.

P.S.- The floor matt makes a great "cruise control" when jammed under the throttle pedal

Dom

 

This is really strange....slightly off-topic....but, I had a dream last night that I was out in the GT4 just cruising around town. I stopped for a red light, and when it turned green I ran 1st up to about 4000 RPM, shifted into second and floored it - and then the throttle stuck! When I let off to grab 3rd, it just kept revving!!!

The thing is, it was one of those dreams where I never thought to just shut the car off or push the clutch in and let the motor grenade -- no -- it was the kind where I was trying to control this out-of-control beast through traffic on city streets!

Maybe this thread, combined with my dream, is a sign....

Aaron

 

David,
To disconnect the cold fast idle device, all you need to do is remove the rocker arm that goes from the "cam" to the throttle linkage. Done. But this device can be tweaked to produce only a tiny amount of advance when cold, which can actually be helpful. Mine is actually missing (previous owner disabled it by removing, but didn't pass along the parts!) and I have always wondered if it would be good to have. The fast idle on the injected cars which is not particularly adjustable and runs the idle to a searing 2800 RPM when cold is BAD BAD BAD and I disabled it from the Mondial. That was purely an emissions device. Yours is helpful because carb cars do tend to have their idle float around a bit until warm. However, if your carbs are synched and the idle set right, it should still idle while cold, just a bit slower than when warm. I actually find in practice that mine idles around 600 RPM when cold, then heads up to about 1000 or a little more when medium-warm and then settles back to 900 where it is "set" when it is thoroughly warm.

As for the return action....the springs in the carb butterfly valves are the only things that pull the throttle closed again. There is no additional spring on the throttle linkage, which you can confirm with the parts diagram.

Try cleaning and lubing the spring on each carb butterfly, right side of the carbs. They can get crud in between the coils and bind. Clean with spray carb cleaner.

Are you sure that BOTH idle stop screws are set right so that it's not hanging up on one? There is one on the forward bank and one of the rear. You probably know that if you have done a synch.

Next step, loosen the throttle cable at the adjuster on the front cam cover to put a lot of slack into it so you can be sure the issue is the linkage and not the cable itself.

[The idea to check the floor mat is not stupid at all. The first time my car pulled the "Floor mat cruise control trick" on me, I freaked. I was on the highway cruising along, and as I got off the exit and downshifted, the engine revved like crazy when I pushed in the clutch. I thought my throttle cable was stuck. I was close to my destination, so I pulled over, scratched my head, and finally figured it out. Then I felt really stupid!]

Back to the linkage. If you can definitely rule out the cable by loosening the adjuster, I would perhaps disconnect the rear or front linkage assembly to try to narrow down where it is binding. You may have a worn piece in the linkage someplace, like the little ball joints on the ends of the linkage arms.

Hope that helps and report back.

Birdman

 

David,
One last thing. Make sure that the rocker arm connecting the cold idle advance cam and the throttle linkage is not sticking on the pivot. It can get rusty in there and become sticky. Pull the arm off, clean the pivot with scotchbrite, lube lightly, clean the inside of the arm (the hole that the pivot rod goes into) and put it back together.

Birdman

 

Well, that pivot could be sticky too, but I was referring to the one on the rocker arm that goes between the cold idle advance cam and the throttle linkage.

Birdman
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make sure none of the hose clamps get in the way of the linkage or throttle cable (there is a tech bulletin about this).
I would suggest disconnecting the cold mechanism as Birdman suggested. Thankfully the Euro cars don't have all this complex workaround stuff
Not obvious but also important: check that the joints (at end of rod your finger was pointing at in first photo) are not too tight and are well greased. If too tight could result in what you are dealing with, if not greased they will wear out and then you have other challenges with un-adjustable air flow etc.

Gerrit
http://dino308gt4.com

 

Check to be sure you have your throttle stop screws adjusted right.

By the way, I'm calling the part that the "rocker arm" pivots on a "pivot" but I'm sure there is a better name for it.

Birdman
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One consistent comment I get when people see my engine compartment is how clean it is. As if it is supposed to be filthy or something. As far back as the 60's wehn I bought an Alfa 1750GTV, I have always kept the engine etc. spotless. Initially out of respect for Giorgio, my mechanic, then for myself as it is nice to work on a clean engine. You can pay attention to what you are doing instead of worrying about grease and dirt getting into the wrong places. Now I WD40 the Ferrari engine, Passat engine and my wife's Golf engine compartments a few times per year. If something starts to leak or hoses start to bulge, I can spot it easily.

Yep those little wires can be fun, easy to get off, fun to get back on. When I first rebuilt my carbs I took the whole linkage apart. The connecting arm (that the 2 rods and throttle cable connect to) has needle bearings to ensure smooth throttle operation. That too can be gummed up as it is likely never to have been removed since the car was built. This winters project (amongst others) is to replace the 3 balls on that arm, mine are all flat on one side due to prior improper adjustment or lack of grease.
If you remove the arm and rods, you can adjust the rods ends at the arm end, wire them up and re-installthe arm with the rods in one piece. Adjusting the rod ends at the carbs is easier and esp. wiring them up. In fact to adjust the carbs you should have had those rod ends disconnected to ensure the throttle openings are only under control of the throttle idle screws. (This also eliminates interference from the cold idle thingie)
The good news is that once you have adjusted the slack on those rod ends you won't have to do it again for years.

Gerrit

 

WD40? You use it as an engine cleaner?

 

If a throttle appears to be sticking, yet no external cause can be found, it's more than likely the butterflies are not adjusted correctly.

For this the carb needs to be removed, and the spindle screws must be loosened to allow the butterflies to shuffle back to the correct rest position.

This is a last resort... but easily checked by simply disconnecting the relevant linkage, backing off the idle speed control screw and seeing if the butterflies close fully.

if they don't... you need to adjust the shaft/spnidle screws.

Sometimes, the spindle could be twisted or bent, from over aggressive servicing or rebuilding.

Often, a clue to this is where the idle air flow balance screws (the ones with the 8mm lock nut NOT the mixture ones) are dramatically different in their respective adjustment to each other, or where the inter connecting linkage balance adjuster is not set "centrally" enough.

 

VERY interesting! Thanks Phil--I always learn something from your posts!

Birdman

 

WD40, spray on, wipe off and where you can't wipe blow it off with compressed air. Great for hoses, aluminum, etc. I avoid it on the timing belts of course. This assumes there isn't built up grease/oil/dirt. Mind you, the regular use also keeps the grime off.

And many think it is a deoderizer as well.

Gerrit