Seville 03 shaking problems after tune-up.
 

Hey,
I just changed the spark plugs on a Cadillac Seville SLS 03. As soon as I changed the spark plugs the car started to shake at idle (Did not do it before). I plugged the computer to check for codes and there are no codes. The spark plugs I used are Champion platinum and I gapped them correctly...
What could the problem be?
Thanks.
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