Suspecting a DISA issue...
 

Hey guys, it's been a lonnngggg time since I've been on here. I picked up a 97 m3 a few years ago and didn't look back, until, well, I hydroplaned while driving in a straight line on the interstate, and did a 180 into a wall, which left me looking back both literally and figuratively. As I only have a year of college left, and I go to school in Manhattan (pretty much impossible to have a car up there), I went with a 92 318i (sedan) that I was able to pick up for $700. My test drive was in a parking lot full of speed bumps so I didn't go more than 10mph. As soon as I bought the car and drove away, I floored it, and it took at least 10 seconds to get through first gear. DOH! I managed to trace the issue to the AFM (took the cover off of it and measured the resistance as I swept the flap, it plateaued around 20% open angle of the flap). I replaced that and the car now does 0-60 in about 12 seconds (up from about 20 seconds with the faulty AFM). My last 318i did it in a little more than 10 seconds, so I know I'm getting close to having it sorted out. The issue now is that I don't have a whole lot of torque under 4500rpm. My last 318i was also a sedan, but was an m44. It seemed to have a much smoother torque curve. My new (well, old I guess) m42 pulls really strong from 5000rpm to redline, but there is a noticable increase in torque at 4500rpm, and a noticable lack of torque below it. I'm suspecting the DISA valve (stuck in the high-rpm setting), but before I go taking anything apart, can anyone suggest any common issues to look for? I've never touched a m42/m44 manifold, and I can't find any good pictures or descriptions of exactly how the DISA works, so if anyone could explain which part (i.e. location on the manifold) is the DISA, when it is supposed to be open and closed (I know the change happens a little over 4krpm), and how it controls the opening and closing of it, I would greatly appreciate it. I've done some searching but haven't been able to find a clear enough answer. If I can find this info out it will help a lot with debugging it, as I know what would make it operate incorrectly. Also, if you know of any other reasons why I'd have that lack of torque, have at it. I appreciate your input.