My '90 vert started having a surging idle problem intermittently last year. Would start great, but would rev between 1200 and 1500 at idle. At first it was only once in a while, but now it does it almost all the time. Then another symptom appeared recently - after about 10 minutes of running, it runs really bad. Can't hardly pull itself. Sounds like it is on one rotor only. When I move the throttle it doesn't react at all; it doesn't rev any higher.

I have looked for vacuum leaks, but no sensor swaps or anything else yet. I will be looking at that next week. I did swap coils to see if it helped the second symptom; it didn't change anything.

I am wondering if I am fighting with one problem, or two... Could the second issue be an apex (or other) seal on the way out? The engine runs fine again when it is cold (if you can ignore the surging idle); the problem only shows up when it is up to full temperature for a couple of minutes.

Thoughts anyone?