The large low-speed lobes of the Pro Series Camshafts result in more overlap and lower and less consistent vacuum at idle. When the ECU sees this lower vacuum, it tries to compensate by enriching the fuel mixture, making the car idle rough. In order to make the engine idle smoothly, it is necessary to reduce the fuel by 20%-30% in the 0-1500 RPM range of the fuel map. To get the smoothest possible idle, we recommend tuning by throttle position. Please note that if the cams are not degreed into their proper position, it may make getting the car to idle more difficult; therefore, in order to optimize power output and minimize idling and clearance issues, we recommend that all Pro-Series cams be degreed in.