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Rough idle

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Old Sep 16, 2025 | 10:58 PM
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Default Rough idle

Hi,
'98, 96000 miles, manual.
Just installed new iridium plugs and MSD wires.
Car accelerates better, more smoth but after engine warms up idle is sort of rough...meaning 5-6 sec smooth followed by an 100-150 rpm drop in idle than fluctuating back n forth to normal fir about 4-5 sec... than repeat.
no other symptoms
any ideas?
Thanks
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Old Sep 16, 2025 | 11:18 PM
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Can be MANY things…see below !!…unfortunately can’t diagnose this for you over the Internet.





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Old Sep 17, 2025 | 01:00 AM
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Originally Posted by C5 Diag
Can be MANY things…see below !!…unfortunately can’t diagnose this for you over the Internet.




wow...this all started after recent plug and wire job...
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Old Sep 17, 2025 | 02:57 AM
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If you still have the old plugs and wires , try to reinstall first wires and then plugs and observe if problems dissappear .
I have my self experienced new plugs was defective from day one and had to be replaced .
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Old Sep 18, 2025 | 10:04 PM
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Today started to hear spark noises as well, beside idling getting worse...
Wire for Nr 8 spark plug was totally off the plug, it came off 2 days after install.
The Corvette tech told me that this is the reason he preffers stock wires: they fit and snap snug on plug. Mine are MSD.
He took a wire plier and push wire down. Hope it will stay.
Car now purrs...
Problem solved!
Interesting thou how strong car pulled with smooth acceleration running on 7 cylinders...
Cheers!
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Old Sep 18, 2025 | 11:24 PM
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As a service tech (not cars) was always taught to start simple and work up from there. An excellent example here,glad it was an easy and cheap fix.
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