Ever since I got my car the tach didn't read right. But during winter it read fine till about 4k rpm. It runs fine most of the time, but sometimes it sticks at about 2k. It may sound odd, but it only messes up at on hot days. Also I had the car for a few months and the throttle cable snaped. After I replaced it, the idel droped to about 100 rpm. Everytime I set it higher its fine for a week or two, then it drops back down to about 100. I've done it a few times and the only thing I can think of is that the cable is stretching.