Idle Issue

MrSony

MrSony

Comic Book Super Hero
Nov 15, 2014
4,902
2,977
113
Des Moines, Iowa
#1
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

MrSony

Comic Book Super Hero
Nov 15, 2014
4,902
2,977
113
Des Moines, Iowa
#2
Could too much fuel pressure cause this too? I have it at 4.5 psi.
 
spidereyes455

spidereyes455

Master Mechanic
Mar 6, 2013
318
288
43
Northeastern PA
#3
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.
 
fleming442

fleming442

Geezer
Dec 26, 2013
6,159
7,052
113
#4
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.
 
TURNA

TURNA

Geezer
Jul 24, 2009
7,460
10,067
113
Socialist NY
#5
When you turn on electrical items in the car the engine acts up???

Sounds like a drain somewhere
 
MrSony

MrSony

Comic Book Super Hero
Nov 15, 2014
4,902
2,977
113
Des Moines, Iowa
#6
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

pontiacgp

Canadian Prime Minister
Mar 31, 2006
24,741
10,202
113
Kitchener, Ontario
#7
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
 
Clone TIE Pilot

Clone TIE Pilot

Royal Smart Person
Aug 14, 2011
1,970
568
63
Galaxy far far away
#8
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

pontiacgp

Canadian Prime Minister
Mar 31, 2006
24,741
10,202
113
Kitchener, Ontario
#9
The A/F gauge you bought will help you determine if the idle problem is caused by a vacuum leak
 
airboatgreg

airboatgreg

Royal Smart Person
Oct 2, 2016
1,545
1,424
113
#10
Wore out throttle shaft on the carb or maybe sticking/leaking secondary throttle plates is my guess
 
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