[mattfranklin]

Do it in stages. First new plugs. Then try cap, rotor, plug wires, and so on, doing the easier cheaper things first and note what happens in each step.

And I saw the comment about a loose carbon deposit that might have closed a spark gap too tightly... Here's a shameless plug for one of my employer's famous products: Techron Concentrate. Use a bottle at the recommended treat rate of 1 oz per gallon of tank size.

Dump a bottle of Techron Concentrate in your fuel tank and fill it up with gas. In the past I've done lots of lab testing. It's a very gentle and persistent cleaner. It should clean your intake valve and combustion chamber deposits. Run it for a tankful of mild around-town driving. Also, we've seen that the second tank after that, even if you don't add any Techron still keeps cleaning, because of the "heel" left behind from the first tank that had the full dose. One set of experiments I did showed a solid restoration of 5-6% of power and torque. We also checked flow bench with dirty intake valves vs. cleaned ones and vs. new ones. Both flow and swirl numbers were significantly improved and similar to the numbers with brand new valves.