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Rough Idle when engine is hot, SOLVED

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Old 11-03-2011, 12:01 AM   #1
BroCorvette
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Default Rough Idle when engine is hot, SOLVED

So I was working on the vette again cause the rough idle when hot came back. To explain exactly what was happening, intermittantly when the motor had a load on it the idle would get rough and it sounded like a cylinder was shutting down for short periods. Usually when I work on the car I have tons of lights on so I can see better. Well i was over at a freiends house tonight and we didnt have much light and it started to do it again. I suddendly saw a light but wasn't sure so was shut the rest of the lights of an kept stairing at the motor and sure enough we saw it. A spark plug was arcing through a plug boot right to the heads. There was a micro scopic hole in the boot. So i just happened to have some industrial glyptall paint on hand. So we through some on the boot and reinstalled it. The car idled so rock solid that the numbers weren't changing even a digit. The spark plug has some white pitting corrision on the bolt section on it so tomorrow ill replace that spark plug but the glyptall paint on the boot solved the problem. After months of searching just waiting till the sun went down and the lights were off solved my problem. Has anyone heard of this before?
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Old 11-03-2011, 08:04 AM   #2
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Good work figuring it out
yes i have had my no.6 spark plug lead insulator get too hot with the exhaust and fail quite often, i keep a few straight insulators in my garage.
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Old 11-03-2011, 08:58 AM   #3
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Seen that happen many times. When I don't see it and I feel that it may be the problem, I use my grounded test light and drag the probe across the wires and boots. The spark now has an easier route to ground and you can see and hear the miss, without getting shocked.
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Old 11-03-2011, 12:52 PM   #4
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I had that kind of problem when it was damp. Found the boots and wires leaking so I replaced all of them and the plugs. No more problem even going thru a car wash.
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Old 11-03-2011, 01:16 PM   #5
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Quote:
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The spark now has an easier route to ground and you can see and hear the miss, without getting shocked.
Wheres the fun in that ??
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Old 11-03-2011, 01:40 PM   #6
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Wheres the fun in that ??
Too many scars on top of my head, from getting blasted by my 68 camaro's ignition(accel coil and msd), then slamming my head into the hood.

Must be getting old or wiser.
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Old 11-03-2011, 01:59 PM   #7
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So far that's the only one that does it. Ill have to look into getting new plugs and high quality plug wires sometime in the future. Any suggestion on best plugs and plug wires?
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Old 11-03-2011, 07:37 PM   #8
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Quote:
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Too many scars on top of my head, from getting blasted by my 68 camaro's ignition(accel coil and msd), then slamming my head into the hood.

Must be getting old or wiser.
I did the same thing on a Austin Healy Bug Eyed Sprite racing car. That f'ing hurts!
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Old 11-04-2011, 03:10 AM   #9
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I did the same thing on a Austin Healy Bug Eyed Sprite racing car. That f'ing hurts!
Try a Jacob's ignition on a 9C1 Caprice!
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Old 11-04-2011, 09:50 AM   #10
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Back in my drag racing days I learned not to grab a Vertex Magneto by the cap when sweating. If you have never worked with a magneto, one small twist of your wrist will send a blue spark across a one inch gap with ease so you can imagine what it felt like at idle speed. That's why they make those plastic covers for them.
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Old 11-04-2011, 10:42 AM   #11
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Had the "rough idle blues" once on my old Mustang after doing a full cap, rotor, wires and plug thing. Ran worse......couldn't figure it out untill I opened the hood BEFORE I turned on the light one night! What a light show! It looked like one of those lightning globes they sell at Spincer Gifts! I had bought a set of cheapy A.Z. wires they were running a special on. Yeah, they were special alright. Special junk! New set of quality wires and fixed everything that had me bugged for a week.
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Old 11-04-2011, 09:35 PM   #12
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Quote:
Originally Posted by aklim View Post
I had that kind of problem when it was damp. Found the boots and wires leaking so I replaced all of them and the plugs. No more problem even going thru a car wash.
Whats a car wash?
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Old 11-04-2011, 11:43 PM   #13
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yep. but then I am an old fart.
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Old 11-05-2011, 09:05 AM   #14
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See it all the time at work... prob 2 or 3 times a month...

Glad you figured it out! Sounds like its time for a basic tune up

Good luck!!!
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Old 11-05-2011, 03:04 PM   #15
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NGK Iriduim IX Part Number # 739-UR5IX
Street Fire Plug Wire Set Part Number # 121-5563



Plug Wire Set BOSCH Part # 09679
Spark plugs BOSCH Part # 7975 SUPER PLUS


I'm torn between these two sets there is a 50 dollar price difference between the two. What are your opinions on these and maybe if you have a better alternative suggest it. Thanks.
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Old 11-05-2011, 03:45 PM   #16
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I used MSD wires and NGK plugs
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Old 11-05-2011, 09:44 PM   #17
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Why would you want to put those crap Bosch spark plugs in?????

Use the NGK - I've used the V and G in all my vettes
Also I used Taylor Spiro pro wires.
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Old 11-06-2011, 04:24 PM   #18
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MSD-5563 MSD 5563 Wire Set, Street Fire, 84-91,Corvette,350TPI

NGK-UR5IX NGK UR5IX 14mm Iridium IX Resistor Projected Insulator Spark Plug Tapered Seat Stock# 7177


Ordered and being ground shipped UPS Monday! Here's to hoping that this combo does better.

Anyone know off the top of their head gap size for these plugs to an 85' ?
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Old 11-06-2011, 10:22 PM   #19
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.035
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Old 11-06-2011, 11:34 PM   #20
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Quote:
Originally Posted by Midnight 85 View Post
.035
Thanks!

I'll let ya'll know how it turns out. Weather is gonna be bad through Thursday next week so she'll probably sleep in the garage till the new plugs and wires come in.

Now if I could just find a way to keep the damn birds out of the garage.
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