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Discussion Starter #1
I have a 2003 impala LS with 3800 II it has been idling rough I was getting a P0300 random missfire so I changed plugs, wires and icm I'm now only getting code P0303 and freeze frame shows it only misses at low RPM 750-850, runs great at speed! All kinds of power! so I changed the plug on 3 and the wires again no fix there. I also changed the lower intake gasket and the whole upper intake. This rough idle is hard to diagnose... Would bad compression cause missis at idle and not at speed? Or fuel injector?

Any ideas?

I'm stumped!
 

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8th Gen Antagonist
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13,660 Posts
Anything is possible, but I would start with spark. So you've eliminated plugs and wires as a cause, test the #3 coil, I wouldn't be surprised if your problem was there.
 

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Injector would be my next thing to check.
 
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