Idle Issue

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MrSony

Geezer
Nov 15, 2014
6,792
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Des Moines, Iowa
For some reason... My idle wont stay consistent day to day. One day it will idle fine at 750 in Park next day it idles at 500 and next 1000. Having the headlights and blower on decrease rpms by about 100 so I lways adjust it at temp with everything off. I think the hot idle screw spring may be weak and backing out. I took a pic of where it is. After a few days or the next time it acts up I'll compare. I may have a vacuum leak as well... I had like 16" of vacuum and it doesn't fluctuate more than 1.25" (276/281 adv dur 112lsa) either way. I guess if the idle changes without the screw moving that will infer a vacuum leak. Or potentially timing jumping/sticking. I'll report on my findings in the coming days.
 

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MrSony

Geezer
Nov 15, 2014
6,792
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Des Moines, Iowa
Could too much fuel pressure cause this too? I have it at 4.5 psi.
 

spidereyes455

G-Body Guru
Mar 6, 2013
776
1,614
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Northeastern PA
At 4.5 psi I would rule out fp being too high. First thing I would look for is a vacuum leak, carefully spray wd40 or similar or water around the intake/ vacuum hoses while its running. Wd will make it rev up water will go down. If that comes up with nothing I'd look at possibly the mechanical advance weights or vac advance canister intermittently sticking. You could also adjust the idle screw an give it a drop of loctite to hold it in adjustment to rule that out.
 
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fleming442

Captain Tenneal
Dec 26, 2013
13,046
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As well as you have that carb dialed in, I'd start looking at the distributor weights. Give them a good deburring on a flat sanding board or with a file and lube the pivot pins with powdered graphite.
 
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TURNA

Rocket Powered Basset Hound
Jul 24, 2009
10,941
19,990
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Socialist NY
When you turn on electrical items in the car the engine acts up???

Sounds like a drain somewhere
 

MrSony

Geezer
Nov 15, 2014
6,792
6,677
113
Des Moines, Iowa
When you turn on electrical items in the car the engine acts up???

Sounds like a drain somewhere
it doesn't really act up, the idle just goes down. volt reading doesn't change, though.
 

pontiacgp

blank
Mar 31, 2006
29,270
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Kitchener, Ontario
I would check the base gasket and if there is no vacuum leak there I would remove the vacuum feed to to the brake boost and plug that hole to see if that is causing a vacuum leak
 
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Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
3,831
2,568
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Galaxy far far away
There are 3 different idle speeds. Cold idle which is 2,000 rpm, curb or normal warm idle which is 600 rpm, and the A/C idle speed which is 1,000 rpm when thd kicker is on. All idle speeds are checked in drive with parking brake on. Putting it in park will throw your readings off, it must be in drive. Must likely problems are vacuum leaks. Sometims both the carb mounting gasket and airhorn gasket need retorquing after a few heat cycles. Check thd carb mounting torque while it is hot.

If you still have CCC, you can find vacuum leaks fast with a dwell meter and a can of carb cleaner. The ecm will react to any change in the A/F mixture from sucking cleaner in through even the slightest leak. You will also need a Mityvac to check all the vacuum diaphragms such as the choke pulloff, brake booster, vacuum motors, EGR valve, etc. Even a bad PCV grommet in your valve cover can lean out your idle.
 

pontiacgp

blank
Mar 31, 2006
29,270
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Kitchener, Ontario
The A/F gauge you bought will help you determine if the idle problem is caused by a vacuum leak
 
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airboatgreg

Comic Book Super Hero
Oct 2, 2016
2,863
3,112
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Wore out throttle shaft on the carb or maybe sticking/leaking secondary throttle plates is my guess
 
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