Anybody have an idea what could cause heavy blue black smoke off idle and up about twice a month? It lasts for about 30 seconds then straightens out and runs normally. This truck is the '91 in my signature that I sold to a buddy, so I'm trying to do this remotely. Pump has about 130,000 miles on it. Performance enhancements have been done. Truck just barely runs when this is happening. Sometimes turning the truck off and restarting it fixes it also.