308 QV Throttle sticking but not the cable

Happened to me once on my QV and the cause was a frayed cable at the end toward the pedal. Image Unavailable, Please Login

 

I had something similar happen, but it was in-fact the throttle cable. The cable sleeve had rusted in the middle; causing resistance at higher throttle. It wasn't an issue at low throttle.

 

Take out the floor mats.

 

Check that the pivot socket at the throttle body end of the cable is not too tight on the ball on the throttle body lever - If the socket is sticky, it can jam the cable at an angle and hold the throttle open when the throttle is released.

The end of the pivot socket has 3 slots in it for a screwdriver to adjust the tightness - check that it swivels/rotates easily. If not, unscrew the end piece, clean and lube the ball socket and inside the cable end pivot, then re-assemble - ensure it's not too tight on the ball socket.

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Gordon

 

Not insisting it's the same as my problem, but most of your "it doesn't happen when I do X" also applied to me. 2k is basically idle. Manually turning the throttle crank (near the intake) doesn't move the entire cable, just the shortened part after where it's mounted.

One way I could reproduce was to turn the engine off, and then push the pedal all the way to the floor. Does it snap back, or sit there with slack / flop?

 

Well the only difference between driving under load and free revving in the garage is the torque applied to the engine and the subsequent movement relative to the chassis. One end of the cable is attached to the chassis and the other to the engine. So I'd check the mounts and the dogbone bushings.

 

Just be clear, you have a QV right not a Carb?

 

Have you ever created the condition, stopped the car (but with the engine still at the high RPM), and looked at the throttle mechanism to confirm it is being held mechanically open off the idle setscrew stop? If it is, it would give you a chance to wiggle/touch it and see if the cable is tight and holding it open or if the cable is loose and it's something else -- just a thought...

 

Plunger sticking in the fuel distributor?

 

Inside the fuel distributor is a plunger that moves up and down, which is what meters the fuel to each cylinder fuel line. This plunger moves inside the unit, which has o rings inside for each cylinder port, which can deteriorate and cause the plunger to stick. The fuel pressure would increase and change with the car under load, which might explain why the condition can't be replicated at rest?

The lever like mechanism connecting to the air plate in the fuel injection unit is what pushes this metering plunger up and down based on air flow into the unit. The amount of motion is very small to make large changes to the fuel delivered, maybe half an inch of plunger travel.

There could be some fuel deposits inside the unit also causing things to stick.

Perhaps run some techron fuel injector cleaner, if it is a fuel deposit issue this might clear things up. Or run some Marvel Mystery oil in the fuel, that would also loosen up deposits.

But as likely the fuel distributor would need a rebuild. There are kits to do this on ebay, the project is doable for a meticulous do it yourselfer. But most would use a rebuilder fellow in the US who is the go to for this.

There is no easy way to test for the sticking problem other than removing the unit and inspect things. The unit can be removed and you can push the plunger up and down and you might feel the stickiness. You could first try to gently press the air flow flap under the air cleaner on the fuel injection unit by hand with the car off, and get a feel for the plunger movement. When you push down, the other end of the lever is pushing up on the plunger at the bottom of the fuel distributor, ie. The part where all the fuel lines are connected.

If your fuel distributor has never been rebuilt it is probably time to do it anyway. The alcohols in modern fuels takes a toll on the old internal rubber o rings and diaphragm.

Given you appear to have exhausted the sticking throttle cable and throttle body idea, I thought it useful to suggest what else could cause the "cruise control" effect. I would probably still remove the throttle cable completely and inspect it before concluding on that being the issue or not. A tiny fraying of the cable could hang things up, although I would expect you could recreate that while the car is at rest. The throttle body itself sticking would also be something I would expect you could recreate at rest.

 

I have to think through the full system interactions. There is the throttle body air bypass that allows air at idle, and the stuck plunger would be giving too much fuel, so you run rich. Take out an accessible spark plug and see if there are signs of running rich.