How did you make out with your problems?
I'm having a similar problem. I'm having a shuddering when I'm driving, rough shaking (not violent yet) on idle. At first, I thought it was a spark plug wire that was loose. I checked, and #5 was indeed loose, but I plugged it back down; still the same issues.
I decided to change the sparks. They were the same model number as the TSRM for an NA except, they had the "S" at the end, instead of the "P" as recommended (Standard vs Platinium I presume). One thing I noticed when I took off the spark plugs closer to the firewall. They were soaked with oil. #'s 1 & 2 were not. Is that normal? I'm going to assume it's not. I couldn't get to 3 &4, really hard to take off. The way the TSRM says to get it off is just ridiculous, and I was also looking for w writeup on changing, but I didn't find one for the NA car.
But anyway, the shudder/idle/the way the car drove was a little better, but not great. Just better than before.
Another thing I noticed: when I took the oil cap off whilst the car was idling, it almost cut off, like the idle would go down to like 300rpm. But as soon as I put it back on, it would go back up to like 7-800rpm. So, that's my symptoms. Is that similar to what you have, or could this be a vacuum leak? No visible signs of a bad or broken hose for leaking...
