The float in your carburetor is bad. Rebuild carb completely and double check float level setting before reinstalling on car.
After doing a little research, your vehicle was never built with a carbureter. All 914's came Fuel Injected. I think the high idle is a mask for other problems with your vehicle. I suggest you bring the vehicle to a mechanic and have it checked out profesionally, rather than wasting time and money floundering about, and not get the car ever running right.
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