The gremlin is still out there, but it is now more clearly ignition related. That makes life much easier. And changing the vacuum line was not a waste either.
How old are the plugs ?
A cheapo brand will not cause these problems per se. They just might not be as optimal for your engine as oem ones.
There are two schools of thought on these forums when it comes to plugs. Some people think that the single or dual-claw oem copper plugs are the best. Others prefer to use the 4-claw platinum iridium non management long life spark plugs instead, which last for 100k. Bosch sells both. The price difference between both is insignificant for practical purposes even when you multiply it by 8.
You could also have a leaky valve cover gasket that fills some of the plug wells with oil. When this happens, the ignition charge's delivery is affected. It could produce these symptoms too I suppose. You might want to remove the spark plug concerned and clean it with carb cleaner if the threads are oiled up. The solution is to extract out any oil using cleanex, then eventually get your vcg replaced properly (there are ways to screw up the reinstallation, please use the manual for correct instructions.)
If your spark plugs are old, and your vcg (valve cover gasket) is not leaking, just change the plugs out to a new set. Small money. Even if this does not solve the problem, you are likely to get a slightly improved performance from your engine.
As a worse case scenario, your ignition coil(s) could be busted. They do not always produce a fault code when they are buggy. Bentley has coil resistances that you can check. Check out the low hanging fruit first before you come to this.
Last edited by robertobaggio20; 11-18-2012 at 08:57 PM.