[TR] Strange engine miss

[John Gillis]

While still trying to get my TR2 engine to run smoothly, I noticed  
this- it seems the engine is running on 3 cylinders due to the rough  
idle, I discovered if I pull the plug cap off No2 plug while running  
there is no change in the rough idle, however when I bring the cap  
near the plug but not actually pushed into place the engine picks up  
and runs smoothly, and when I push the cap fully home the rough idle  
returns. Any ideas?
John