I drive a 1998 mercury sable which really is the same thing as the 98 ford taurus, as we found out both of our onboard ECM's have a serious flaw in them. (electronic control module, the "computer chip" if the car, which actually isnt a chip, it's a big silver box that sits in the firewall) For some reason, the stock ECM units would not throw a signal to the transmission to "downshift" when going down a hill, and the car would just run away like it was coasting down the hill in the overdrive gear. Installing a new ECM with an update fixes this problem but it's an expensive fix, $400.00 US. Plus, the new ECM's gave our cars about 5-10+MPG, and saves on the brake shoes as well.
I am not impressed with it though as on some occasions, the car seems to drive just fine, but rarely, it kinda "forgets" where it should idle at and just randomly shift into neutral and back into gear again. My dad had the crazy idea of putting 3 bottles of fuel injector cleaner into a fresh tank of gas to see if it would quit that. Strangely enough it did.
