My 1999 Mercury Tracer transmission feels like it engages after 5-10 seconds when the shifter is in the Drive position and the engine is at idle, but it disengages when I attempt to accelerate. When the shifter is in manual first position it engages and drives just fine, and up shifts as I manually move the shifter to 2nd and then Drive. It will then drive fine in D position at all speeds as long as I don't come to a complete stop. If the car comes to a complete stop, I then have to go through the same process again. Reverse always works fine. This all happened after a recent fluid leak. What is wrong?
Problems with the valve body in your 4EAT trans. Valve body is replaceable, from the junkyard, though some yards won't let you pull just the valve body. Done plenty of these: crossmember needs to come off after car is in air, etc. Downshift cable is a pain, but doable. BEST to install a transgo shift kit if you are a mechanical whiz -- tightens shifts, takes out slop, removes the harsh shifting, etc.
BE warned though! If you pull the valve body from your car, sometimes the gasket between it and the case tears or falls apart. Then you need to buy the gasket rebuild kit ($150 plus) Best to just get another trans from the junkyard. Installation is a bear -- the first one is a rough one, but I've replaced about 20 of these transmissions, and with patience you can do it. You need a bunch of tools, trans jack, torque wrenches, patience, etc. Your trans problem is kind of rare, but your valve body is done. Good luck.