308 QV Throttle sticking but not the cable

For it to “hang” does it not imply the butterfly must be partially open? Have you investigated the shaft /butterfly/spring assembly.

The fact it snaps back 4500 might be the return spring being more compressed overcomes whatever is causing the stickiness…..,Maybe!

 

Experience of other cars suggests “load” has some effect which might go some way to explaining why it happens only on the road. Is there anything else that would cause the same effect as the butterfly being open? If not with foot off the accelerator the butterfly should snap back to almost closed (idle speed).

 

Glad you found the solution. Being new to this I think I need to learn more about K tronic!

 

Well if it's the cable the cause would be the opposite of slack because, as I suggested before, under load the torque from the wheels wants to rotate the engine backwards. This is arrested by the dog-bone brace that runs from the top of the 1-4 cam cover to the rear firewall. If you had a blown out bushing in that brace or if the firewall mount came loose and you lost one or two of the slotted shims the movement would pull on the cable which is connected to the chassis. Maybe just grab that brace and make sure it's rock solid. If it is at least you can cross it off the suspect list.

 

Having driven test engines without the brace, I've never experienced that problem. I wouldn't go spirited driving without the brace. The engine also moves a lot more in reverse then forward.

The engine is either getting more air other then the throttle, i.e. a broken or messed up check valve on one of the vacuum circuits or the the cable/TB is sticking.

 

Not only the brace, but also motor mounts.

 

The entire concept of a Bowdin cable eliminates movement of the engine causing the cable to be pulled. Torque strut or not.

Slack or not, same applies. Cable needs slack. Too much only limits total throttle opening.

Its a case of GIGO.

 

Would not matter.

 

You're right now that I think about it, The cable housing is secured to the bracket on intake manifold. Oh well, I was just floating ideas but he can scratch that one off the list.