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Hey folks,

I have a '72 710M, pretty low miles and in pretty good shape. Over the last couple months, it's started idling somewhat fast. Not fast enough that I'm worried the engine will blow, but not right. I can usually tap the accelerator and the idle will lower, but sometimes not all the way. That trick is starting to work less often. Today it got worse, and the idle speed even started increasing on its own. Driving super slow is now impossible, as it just starts accelerating. The linkage all seems unimpeded.

I imagine someone here knows the likely culprit. Any advice?

Check for vacuum leaks.

One hose to the distributor, another to the brake booster, check the
carb mounting bolts didn't loosen up etc.

Thanks! I’ll check those things tomorrow.

Possibly also check the intake manifold balancing hose under the engine tin. Group 1-35, item 60 in the parts book. It maintains equal air balance between the front carb manifold and the rear carb manifold. The hose is exposed to heat from the cylinder heads and begins to degrade over time.

Adding that to the list. Thanks!

So all I did was twist the vacuum hose at the port and distributor, and it's idling nice and low now. I don't see any cracks, so not sure why it worked. Is it safe to assume that installing the PinzSSI I have on the shelf will likely negate this problem, as I will be plugging the vacuum port? (assuming this was the actual issue and not a weird coincidence).

Thanks for yall's help!

Update:
The problem kept getting worse. I replaced all the vacuum lines, including he intake manifold balancing hose (thanks rmel & pcolette), installed a PinzSSI, and had the carbs rebuilt (thanks Goatwerks!). I just finished installing the carbs, and it now runs like a top! Starts easily, has a stable idle and very smooth acceleration. It's a good day.