Colder spark plugs are better suited to high engine loads and perform worse in cold start and idle. Adding E85 or an e flex tune like E30 along with colder spark plugs may make your idle even rougher.
See this video for more information:
Spark plugs have a temperature range that they are designed to operate in. A colder spark plug doesn’t fire colder, but it does help evacuate heat from the cylinder head faster. Pressures with emissions and finding the right balance between a spark plug that will burn fuel completely even during short trips and one that can handle long hard driving is difficult.
Tuner’s note — colder plugs for tuned AMG engines
- Helps prevent misfiring when running high-load
- Prevents spark blowout under higher boost & ethanol blends
- Improved operation at high boost levels
- May make cold start in winter with ethanol blends hard
