I assume you mean spark plugs right? at first i thought you meant the wires on the O2...

I know that if it is black that would be if it was running too rich, what are the signs of lean-ness?

Also I am going to have it taken in for an inspection, would they be able to plug somthing up the tailpipe and tell me the A/F ratio?? If there is such a test let me know so i can have it done.

This is a mystery to me since it only happens at one speed...does it just sound like a fouled O2??

Thanks for the help

Matt