Bad Ignition Coil?

Hi,

I have been having some recent issues where the rpm's are fluctuating. I'll be sitting at an idle or driving and the rpm's will just suddenly jump. I recently replaced one of the ignition coils due to corrosion issue on one of the terminals. Could the coil be bad? Any ideas how to test the coil if that could be the issue? (I also replaced the plugs and wires along with the coil)

2001 Pontiac Grand Prix GT 3.8?

Thanks

What do you mean by jump?

Does it misfire under a load on the highway?

You test coil output with a spark tester......

I've never used a spark tester before. How does that work?

As for the "jump," when idling (waiting at a red light) the rpm's will move from 800 to 1200/1300 rpm. The same thing happens when driving in different gears. It seems like a misfire but I just replaced the plugs/wires and one of the ignition coils. I thought the transmission was slipping but you would have some sort of consistency with a slipping transmission. This issue does not happen every time while driving.

Thanks

That is too much of a jump for a misfire......I would be checking for a vac leak, IAC problem, etc.