Hello guys! I am new to this forum. I recently purchased a 1997 STS. I knew nothing about the car when I bought it. It has 175,000 on the odometer. When I bought it, it wouldn't run and I narrowed it down to the fuel pump and replaced it. I have it running now but it is running very rough. The guy I purchased it from said someone told him it was the head gasket. I found out that the reason the cooling system wouldn't hold pressure was it was leaking around the reservior neck where it attaches to the tank. I replaced that and everything looks good. I don't know when the plugs or wires have been changed last. After I got it running, it had a missfire code for cylinders 3 and 4, but you could pull the wires off of 2 and 4 and it didn't make any difference in the way it idled. I really feel that it is something simple to fix. I have searched on here and found many threads about the problem but it seems no one ever comes back and posts the cure to there missfire. I have reset the codes and driven it about 20 miles and the only code now is the generic P0300. I know I will get several responses saying to change the plugs and wires and that it could be a bad coil. It there anyway to narrow it down instead of changing all of those at one time? I checked the intake bolts and all were tight on them. One thing that I did notice is that is sounds like an airpump noise around the intake. It almost sounds like it is sucking and blowing with the stroke of the engine. I have sprayed ether all around the intake but it never made a difference. Can you guys point me in the right direction so I won't have to spend a lot of money replacing several parts when it could be just only one causing the problem? Thanks for your help gentlemen!