Rough Idle/Mis Fire after new plugs and wire

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Aug 10, 2020
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I had my mechanic replace my plugs and wires on my 96 LC. I used the kit from Wits.....all OEM stuff.

When in Park, my RPMS were all over the place....pretty rough idle.......no issues when driving. So I took it back to the shop, they said it seemed like a misfire. They ended up putting the old plugs and wires back on and said the problem went away.

Any thoughts on this? I'm scratching my head.
 

florida95fzj

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Were the old plugs OEM? If not, was the timing previously adjusted out of spec so that it would work better with the old (wrong) plugs? I would see how the timing is set.
 

florida95fzj

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The advice from @drew1320 makes the most sense. A new plug or wire could just be bad/damaged. Although I am assuming they looked at them to be sure one is not cracked and they are all gapped correctly. I don't know of the right way to test the wires short of testing for continuity which may not tell you anything useful.

I would still have them check the timing if you don't know how it is currently set.
 
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Another issue that happens often and more lately, counterfeit parts made in china that are knockoffs. They look the same and get into the supply chain without techs, shops, and parts suppliers ever knowing. I have been a part of identifing counterfeit parts (plugs/filters) and its almost impossible to sort out the real from the fake.
Just a thought. The shop could have installed bad parts without anyone knowing.

You can test a plug wire with a resistance test but thats not totally accurate, it could have issues that only show during operation.
 
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I had a similar issue with RPMs all over the place and a miss firing engine. Replaced MAF sensor and the issue persisted. It ended up being burned cooper leads on the ECU. You may want to open it up and see if it's ok.
 

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