I have a 96 olds bravada with 4.3L v6 Vortec. When I start the engine it will sometimes rev as high as 3000 and stay there for a few seconds to a full minute before returning to a normal idle rpm. I have seen other vehicles rev up when they are first started, but none that stay that high for as long as mine does. It also has a problem with shuddering when I put it into gear. It doesn't seem to be a problem from the transmission, but yet more as though the computer can not decide on an RPM to idle at once the vehicle is in gear. This problem only happens every now and then, and only lasts for maybe a minute then returns to normal. I replaced my throtle possition sensor last year hoping to solve the problem, and I have still had the problem since. There are other times when I put the vehicle into gear that it will rev up to 1500 without me even touching the gas and stay there for a minute. If i let off the brakes and let the vehicle start moving, I can drive a mile or better before the idle will drop back to normal. If I set and hold the brake for a while, than it will drop to normal. I hope someone can understand this problem and give me some feed back. I should also point out that this happens at complete random times. It doesn't matter if it's winter and 20, or if it's summer and 90. Raining or dry also makes no difference.