Slightly Rough Idle

[DMBuck]

2009 GT. Only engine mods are a K&N CAI, Bassani Axel Back exhaust, just added Accel Super Coils 140033-8. Car starts right up, runs great at speed, no obvious miss or hesitation. When at the lower idle level shortly after the higher start-up idle, engine seems to idle ever so slightly rough. Somewhat intermittent, about every 10 seconds or so just a touch of roughness. Any ideas? Thanks,

 

[mustangdave]

My guess would be the coils; the factory units have proven themselves to be better than aftermatket units.

 

[DMBuck]

Thanks. Only 6K miles on the car. Old coils back in similar low idle roughness. New coils back in, fresh tank of premium, bottle of Lucas. We'll see what happens. Ethanol causing this? Car is only a weekend driver...

 

[jpplaw]

Is the roughness something new? Or did it always do it? The stock cams are ground for torque, and are actually pretty darn good. However, they do not idle perfectly smooth even when there is nothing wrong. There is a very slight cam lope even when stock.

 

[DMBuck]

It's always had just a touch of roughness. No miss, nothing you notice at speed, just at low idle. I thought the new coils would eliminate. When you stare at the plenum, it looks pretty steady, then about every 10 to 15 seconds, you notice this slight wiggle/roughness. Does it with the stock and Accel coils.