72 911S engine speed comes down very slow.

[silver72S]

Hi, guys
Today, I drove my 72 911S after a summer storage of a few months as it was too hot to drive it without the air conditioner.
I found that the engine speed did not come down quickly as it did before the storage.
I tested the rpm system and found the engine speed hunted between 1300 to 2500 rpm with pressing down on the microswitch.

What else should I check?

Thanks in advance.

Takahiro

[bliebler]

pull off dist cap and suck on vacuum line and see if plate moves. The vacuum retard may not be pulling down idle. Blow all lines out and clean out ports on mfi stacks with pipe cleaner.

[30westrob]

I have seen this issue on MFI cars caused by throttle linkage. If you can pull the linkage from the engine compartment and return the engine to idle, then your problem is in the linkage. Probably light corrosion or old grease, and time to clean and lube. Rob

[dporsche74]

gummed up...

[rdelmendo]

Hi Takahiro-

When the engine is revving high, can you drop it back to normal by pulling back on the gas pedal with your toes? If so, 30westrob and dporsche74 are spot on and you have schmutz in the throttle linkage.

[silver72S]

Hi guys,
Thank you for your suggestions. I will suck on the vacuum line and check the linkage moves freely.
I will report them here.

Takahiro

[silver72S]

Hi guys,

I tried sucking on the vacuum line on the distributor and lubed the throttle linkage on this weekend. I could not get any good result though.
My symptom was that the engine speed did not come down quickly from 2000 - 3000rpm, but came down quickly from 5000+ as normal.

I suspected that the rpm transducer did not work properly while I was driving. After came back home, I exchanged it with backup rpm transducer.
It worked well, and the engine speed came down quickly as it should.

Thank you very much for your information.

Takahiro

[dummkopf]

I would say the linkage points need to be lubed. Mine is a 72S converted to Webers, and I recently have experienced the same problem. I can "pop" the pedal and it will idle down. That is the next thing on my list. Lube the linkages and joints.

[72t4tom]

I am having the same problem. I sprayed some rust solvent on the coil springs at each butterfly. there should be 6 of them. It will help a little bit