At 4K the engine begins to miss and stumble (similar to a rev limiter kicking in) as well as having 450-500 rmp Idle. Just replaced EGR valve. Fault code is 6 per the LED reader on the car. (the EGR valve cleared the 5 I had). Is this the ISC faulty code? If so, what part is it? I've searched the forum and can't find anything specific to the E420 on this.