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#1 |
Registered User
Join Date: Feb 2009
Location: Jefferson City, MO
Posts: 83
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Miss At Idle
I have an odd miss at idle - it runs fine when the engine is cold or cool, but once it warms up it has a miss that sounds more like "thunka thunka" than just a dead spot. No knocking, etc. It almost sounds like a plug wire crossed, but I've checked them several times. I've also made the idle richer with no change. The longer it runs, the worse it gets, until you can feel the truck shake a little at idle. Runs great going down the road.
Stock 350, 70,000 miles, HEI, new cap, plugs, wires, rotor, 10 gauge wire from fuse box to dizzy, timing set to low 30s at full advance. Thanks Last edited by mdwilf; 07-07-2010 at 09:40 AM. |
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#2 |
Registered User
Join Date: Jan 2010
Location: yuba city ca
Posts: 31
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Re: Miss At Idle
Check for a vacuum leak around the intake manifold where it bolts to the head. Spraying with starter fluid.
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#3 |
Registered User
Join Date: Jun 2010
Location: Upland Ca
Posts: 4,143
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Re: Miss At Idle
Sounds like a bad plug wire, maybe a burnt boot. When warm and missing, I would start removing wires one at a time. As you remove each wire the engine will miss more, those wires are alright. You've found the bad one when the miss does not change when the wire is removed. Replace that wire and all should be fine. I would check the plug in that hole to make sure it is not fouled. Also make sure wires 5 & 7 are not touching each other, keep them separated from cap to plug.
__________________
1972 C10 SWB, Air, PS, PB, 350/350THM. Second owner. 1965 Corvette roadster, 44K miles, 327/365 SHP, 4 speed, side exhaust, knockoffs, teak, second owner (bought in 1970), Have ALL numbers matching components. My frame off restoration thread: http://67-72chevytrucks.com/vboard/s...d.php?t=556703 |
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#4 |
Registered User
Join Date: Oct 2005
Location: Overland Park, Ks.
Posts: 5,219
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Re: Miss At Idle
Have you run a comp. test. Sounds like a week valve to me. It's possible one is adjusted too tight.
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#5 |
Account Suspended
Join Date: Jan 2007
Location: Tucson
Posts: 2,183
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Re: Miss At Idle
You did not say if you're running an automatic choke, but if you are I'll bet the farm on a vacuum leak. When the engine is cold the choke is closed providing a richer mixture at idle. When the choke opens the mixture should lean out to the correct stochiometric air/fuel ratio but if there is a vacuum leak the mixture leans out way too much when the choke opens and you get a very rough idle.
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#6 |
Registered User
Join Date: May 2006
Location: Jonesboro, AR
Posts: 916
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Re: Miss At Idle
I'm guessing it could also be a head gasket leak.
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#7 |
Registered User
Join Date: Nov 2007
Location: Marion, IL
Posts: 112
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Re: Miss At Idle
Had the same problem - turned out it was a leaking brake vac. booster. Plug the line and see if the idle improves.
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#8 |
Registered User
![]() Join Date: Feb 2009
Location: Indianapolis, IN
Posts: 372
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Re: Miss At Idle
I had a similar problem...except mine would also miss out with WOT .....I changed the plugs and I was good
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