Has anyone heard of roller lifters sticking? My vacuum gauge fluctuates terribly below 1500 rpms. It has done this since the rebuild and installation of a Comp 212/212 roller cam. The work was done by a reputable shop known for Buick Turbo 6s. The engine seems to idle a little rough and rich, compared to stock. I can't find any vacuum leaks. The rebuilder says they have had some quality issues with some of the lifters. I think he said they were being produced in Mexico. Has anyone experienced this? Is there a way to check them, or narrow it down to a particular cylinder? Any help would be greatly appreciated. Dave C.