I rechecked, my coil replacement was an Accel but looked identical to the Ultima but has worked for 2 plus seasons, ya the Ultima did drop one of the cylinders also at idle.

Single fire coils are 3 ohm, look for something along that line but don't buy into the 45,000,000 volt advertisements, basic coils will work fine and I believe coil housings have seperate coils in the housing and must be a cooling thing for seperate external coils, hopefully someone can answer that question.

 

You can also adjust the curve more precisely and download the usage statistics with a laptop.

See here for more info: https://sites.google.com/site/vrusb2000i/

 

Any coil so long as it falls within the correct ohms range, which i believe is around 3 Ohms but you can double check on the Ultima web sites in their instructions.

I have run the same Dyna S Single fire units for 15 years woth no issues - they are a well made reliable piece of kit. I assume the modern ones are still made in the USA; if they have offshored them, then it may pay to look around.