Fast Idle - Help!

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Fentonite
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Joined: Tue Nov 19, 2013 3:40 pm
Location: Denver, CO

Fast Idle - Help!

Post by Fentonite » Tue Mar 16, 2021 6:10 pm

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?

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rmel
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Location: Woodside, CA
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Re: Fast Idle - Help!

Post by rmel » Tue Mar 16, 2021 6:44 pm

Check for vacuum leaks.

One hose to the distributor, another to the brake booster, check the
carb mounting bolts didn't loosen up etc.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

Fentonite
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Joined: Tue Nov 19, 2013 3:40 pm
Location: Denver, CO

Re: Fast Idle - Help!

Post by Fentonite » Tue Mar 16, 2021 9:00 pm

Thanks! I’ll check those things tomorrow.

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pcolette
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Re: Fast Idle - Help!

Post by pcolette » Tue Mar 16, 2021 11:22 pm

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.
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Paul C.
_________
'73 Swiss 710M
'89 Puch 230GE
2002 MB G500

Fentonite
United States of America
Posts: 44
Joined: Tue Nov 19, 2013 3:40 pm
Location: Denver, CO

Re: Fast Idle - Help!

Post by Fentonite » Tue Mar 16, 2021 11:31 pm

Adding that to the list. Thanks!

Fentonite
United States of America
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Joined: Tue Nov 19, 2013 3:40 pm
Location: Denver, CO

Re: Fast Idle - Help!

Post by Fentonite » Wed Mar 17, 2021 5:07 pm

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!

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