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> Idle fluctuation, Rpm between 1000 and 2000
SWH
post Feb 5 2025, 11:18 PM
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Completed rebuild on 1974 914 2.0 L. All fuel and vacuum lines are also new. Engine idle varies between 1000 and 2000 rpm every few seconds what could cause this?
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brant
post Feb 6 2025, 07:34 AM
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Did you rebuild the throttle body?

Most of them are worn creating a vacuum leak

Also worth servicing the distributor
Or just replacing with 123
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ctc911ctc
post Feb 6 2025, 07:59 AM
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QUOTE(brant @ Feb 6 2025, 08:34 AM) *

Did you rebuild the throttle body?

Most of them are worn creating a vacuum leak

Also worth servicing the distributor
Or just replacing with 123


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Start here - this is the foundation of all things DJet
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worn
post Feb 6 2025, 06:46 PM
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QUOTE(ctc911ctc @ Feb 6 2025, 05:59 AM) *

QUOTE(brant @ Feb 6 2025, 08:34 AM) *

Did you rebuild the throttle body?

Most of them are worn creating a vacuum leak

Also worth servicing the distributor
Or just replacing with 123


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Start here - this is the foundation of all things DJet

I hope that you will expand on your answer. How do the dizzy and throttle body feed into this? Anything that I can learn about the little fellers is a bonus. Thanks.
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brant
post Feb 7 2025, 03:55 PM
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QUOTE(worn @ Feb 6 2025, 05:46 PM) *

QUOTE(ctc911ctc @ Feb 6 2025, 05:59 AM) *

QUOTE(brant @ Feb 6 2025, 08:34 AM) *

Did you rebuild the throttle body?

Most of them are worn creating a vacuum leak

Also worth servicing the distributor
Or just replacing with 123


(IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif)

Start here - this is the foundation of all things DJet

I hope that you will expand on your answer. How do the dizzy and throttle body feed into this? Anything that I can learn about the little fellers is a bonus. Thanks.



I'll take a stab at an answer Worn....


so the TB has the TPS which is how it is calibrated.
the TPS knows when the butterfly is closed, and thus how much air should be entering the intake ... when the butterfly is worn out... air enters arounds the sides of it.

and also... the calibration becomes wrong. as the units of air it is expecting (very little, just the hole in the butterfly at idle) when in reality on a worn out TB, you are getting more units of air than the TPS thinks... that is an unmettered vacuum leak

regarding the dizzy. it has the points plates which slide or rotate and change the timing. those plates need to slide easily. easily enough for the vacuum canister to advance or retard the timing slightly as the centifugal weights pull it in a direction with rpm.

some of these stick... also I've had very worn plates on cars. with a worn or stuck plate they are not returning or opening smoothly ... any time timing is changed, so does rpm.


short answer.
but 2 of the most common causes of surging idle
and not surprising as these parts are 50 years old.

2K is a pretty high idle. I would want to verify the accurate and correct timing. and then I'd expect to find more vacuum leaks for such a high idle.

brant
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Posts in this topic
SWH   Idle fluctuation   Feb 5 2025, 11:18 PM
brant   Did you rebuild the throttle body? Most of them a...   Feb 6 2025, 07:34 AM
ctc911ctc   Did you rebuild the throttle body? Most of them ...   Feb 6 2025, 07:59 AM
worn   Did you rebuild the throttle body? Most of them...   Feb 6 2025, 06:46 PM
brant   [quote name='ctc911ctc' post='3190563' date='Feb ...   Feb 7 2025, 03:55 PM
brant   Dup   Feb 7 2025, 04:12 PM
76-914   [quote name='ctc911ctc' post='3190563' date='Feb...   Feb 7 2025, 05:07 PM
TJB/914   [quote name='brant' date='Feb 6 2025, ...   Feb 6 2025, 04:21 PM
emerygt350   That is interesting, there are not any feedback me...   Feb 6 2025, 11:29 AM
VaccaRabite   I'm going to go with throttle body as the prim...   Feb 6 2025, 01:59 PM
rhodyguy   Known as ‘hunting’? Up and down? Examine the s...   Feb 6 2025, 02:06 PM
914sgofast2   You have an uncontrolled vacuum leak somewhere dow...   Feb 6 2025, 02:18 PM
ctc911ctc   You have an uncontrolled vacuum leak somewhere do...   Feb 6 2025, 02:47 PM
emerygt350   Hunting normally isn't the result of a vacuum ...   Feb 6 2025, 06:53 PM
brant   I hope you’re doing GREAT. Kent It’s been a w...   Feb 7 2025, 07:01 PM
emerygt350   I would go with a leak like brant described if it ...   Feb 7 2025, 09:35 PM
saigon71   A hunting idle can also be caused by a lean idle m...   Feb 8 2025, 06:59 AM
emerygt350   A hunting idle can also be caused by a lean idle ...   Feb 8 2025, 11:06 AM
JamesM   A hunting idle can also be caused by a lean idle ...   Feb 10 2025, 10:28 PM
SWH   Thank for all the feedback on the idle searching p...   Feb 9 2025, 12:53 PM
ctc911ctc   Beautiful Paint Job - do you have a color number? ...   Feb 9 2025, 02:47 PM
emerygt350   remind me, was it modded at all? I bet you are ju...   Feb 9 2025, 02:32 PM
Fazasport   Can anyone reccomend someone who is currently rebu...   Feb 10 2025, 04:13 PM
emerygt350   Can anyone reccomend someone who is currently reb...   Feb 10 2025, 05:53 PM
steuspeed   I had a hunting idle and it went away when I repla...   Feb 10 2025, 11:55 PM


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