Hi this is my first post here. I own a 93 Firebird Formula a4 with a few bolt ons and the car currently has just over 101000 miles on it. Ive had this problem for a few weeks and it is starting to worry me. After driving for about 20 minutes or so the engine will start to miss or hesitate when I try to accelerate in rpms between 1000 and 2000. Is this the sign of a bad optispark or a bad o2 sensor or someting else? I had a water pump failure about 3 years ago and it leaked out all coolant before I could replace it. And if it is a bad opti, is there any guides out there to replace it or is it pretty straight forward?