Changing out some plugs to troubleshoot "vibrating" idle.

[mikepier]

I've been trying to solve a problem with my 99 SOHC for the past few months. As I've posted before in the past, when it is in gear at a light, the engine has what I describe as cyclic resonation throughout the truck. Other than that the truck is flawless on the highway and normal driving. I have checked all vacuum lines and the IAC,MAF, ignition wires. One thing I long suspected was the spark plugs which I put in about a year ago, Autolites APP103 double platinums. From day one I noticed the idle was slightly "different".
Rather than go through the trouble of replacing all the plugs with Motorcrafts, I was thinking of buying just 2 or 3 plugs and replace the drivers side ( easiest side ) and see if it makes a difference. If it does, then I know I'm on the right track, and I'll buy and replace the passengers side. And if it doesn't, then I'm only out $15 since I probably can't return the plugs at Auto Zone. Any opinions?
Also how do I know if my ignition coil is good? I did test it with my ohmeter and it was in spec with the Haynes book, but does that mean the coil is good?

 

[aldive]

Did you replace the spark plug wires when you did the plugs?

 

[mikepier]

Did you replace the spark plug wires when you did the plugs?

Yes, forgot to mention that. I wish I would have done the plugs first then the wires, instead of the same time so I could tell what was the problem, but I would have to buy a new set of wires now to eliminate that as the problem, But I did a test of pulling each wire off the coil while the engine was running and each time yielded the same result, there was no abnormality found.