Ok, so I've replaced the fuel filter, spark plugs, plug wires, PCV valve, some bad vacuum lines, cleaned the fuel injectors, cleaned the throttle body, cleaned the IAC valve, Seafoamed the engine, and checked all my electrical connections and I still have a horrible rough idle. There is no misfire, it's just rough. What concerns me is that I have what sounds like a lifter tap at idle. I say "what sounds like" because I'm not sure that's what it is, but it sure sounds like it. For all of you that say it's a valve seat, it is NOT a valve seat failing. I know what they sound like and it is not that at all. How prone to failure are the lifters or rocker arms in these engines? My 99 has only 86K miles, but something in the engine really taps at idle. Also, when driving, the engine has a weird sound. Almost like a rod or main bearing noise, but for 12K miles, it has not gotten worse. I don't know if maybe it's the lifter causing this odd noise at all. Should I replace the lifters or should I be worried about the oil pump or failed bearings. From what I have been told, the bottom ends and rods in these cars are VERY good and the valvetrain is the weak link. Also, when I rev the engine to about 1200rpms and then let off, all the lifters clatter a bit. Could this be a worn timing belt or oil pump as well? Or just worn out lifters? Any thoughts would be great because this rough idle really sucks.