cowpuncha

I'm currently working on a Mack E7-300, and for some reason it has a surging idle, hot or cold, it's a V-Mack 1. The owner just replaced the throttle assembly but still no difference. Runs fine for appx. 60 second's after starting, and then begins surging. It has no active codes when i hook it up with the laptop. So i was wondering if anyone has any idea's, or has had this problem before. Thanks.