bad idle

What plugs did you put in 3k ago and did you blow the debris out of the plug wells before removing them to inspect them?

You do not need to check the threads per se. What you need to do is go back a few weeks after installing the plugs and make sure they are still torqued to spec, 13-17 foot pounds I believe. Do not actually remove them unless it is really necessary. Also, while doing this be sure to use silicone spray on the cop boots to clean and condition them and ensure a good water tight seal atthe top of the plug well. Also, be sure to use silicone dielectric grease on the spring end where it connects to the top of the spark plug to ensure a good electrical connection.