I have a 1991 Chevy Lumina. It started to run around, is missing here and there. Yesterday, however, to do some big time car started chugging and act like he wants to die. I was to lose power. When I stepped on the gas, I had to push down the gas to go there even a slow, only to come home. The mechanic said that he was connected to a diagnostic computer to test it. . . He said the spark plugs were good. This part is somewhere around the engine block under the coils. Does anyone know anything about it?