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:
Products
-
Android Screen Upgrade
$777.00
-
ModalWorks C63 and C43 Split Cooling Kit Transmission
$784.00
-
blackboost downpipes for c190
$1,699.00
-
PTG V3 Motorsport Cooling System
$4,199.00
-
ModalWorks E63 Split Transmission Cooling
$774.00
