 Idle fluctuation, Rpm between 1000 and 2000 |
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| SWH |
 Feb 5 2025, 11:18 PM
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#1
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Newbie  Group: Members Posts: 12 Joined: 27-April 24 From: Arizona Member No.: 28,084 Region Association: Southwest Region  |
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 |
Feb 6 2025, 07:34 AM
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#2
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914 Wizard Group: Members Posts: 11,894 Joined: 30-December 02 From: Colorado Member No.: 47 Region Association: Rocky Mountains 
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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 |
Feb 6 2025, 07:59 AM
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#3
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Senior Member Group: Members Posts: 1,057 Joined: 9-June 18 From: boston Member No.: 22,206 Region Association: North East States
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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 (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 |
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| worn |
Feb 6 2025, 06:46 PM
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#4
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Winner of the Utah Twisted Joint Award Group: Members Posts: 3,455 Joined: 3-June 11 From: Madison, WI Member No.: 13,152 Region Association: Upper MidWest
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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 (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. |
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| brant |
Feb 7 2025, 03:55 PM
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#5
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914 Wizard Group: Members Posts: 11,894 Joined: 30-December 02 From: Colorado Member No.: 47 Region Association: Rocky Mountains
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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 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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