Ok heres my problem.... Car runs good, but when I need to pass someone, or show off a little my car studders when it reaches about 4,500 RPM. It did it bad for about 2 days, but it kinda cleared up. It was so bad at one point, it wouldn't go over 4,000 RPM. I don't know it just feels like there isn't any power anymore. It happened right after I had my X-pipe installed. It used to surge real bad at idle like 1,000 RPM surge (sometimes it would stall) So I replaced the IAC and it fixed it, but now it is starting to come back. Not as bad as it was, but it still kinda surges. I don't know where to even look. But I need it fixed ASAP. If anyone knows, or has ideas about the problem please help me out. Thanks in advance.