2002 Buick Century 3.1 L V6.
95,000 mi had intake manifold gasket replaced. When left the garage it had a bad miss. Looked under hood at night and saw wires arcing to block from where technician grasped sparkplug wire boot with removal tool thus damaging insulation.
Had wires replaced ? cured miss. But that immediately caused another problem. The car will not accelerate at mid speeds under half throttle acceleration. Say driving steady 35 mph on level road, give half throttle to pick up speed and the engine growls like it is lugging but does not pick up speed. At full acceleration (stomp on pedal) will shift to lower gear and rev up to accelerate. Also when engine cold will accelerate normally at mid speeds using half throttle. As soon as engine starts to warm up (3-5 minutes) the acceleration problem presents itself.
Tried new air filter and cleaned Mass Air Flow sensor with spray fluid for that purpose. Tried unlit propane torch for vacuum leak at idle but didn?t hear any difference. (That doesn?t mean there isn?t a vacuum leak ? it just means I didn?t hear the engine speed up.) In the 70?s many of us shade tree mechanics sprayed either around looking for vacuum leaks but I don?t know if that is dangerous with today?s engines.