 99 Contour transmission problems
I have a '99 ford contour (SE), and I have transmission problems. problems that can lead to
My transmission is unnecessarily downshifting, actually violently knocking into and out of the lower gears. it started with just the overdrive, when it start lightly downshifting for no reason, and only happening over 60mph
My dad got a tip from work that he should add more ground wires to the trans because the existing ground could not be working right anymore, so we did that (we checked out the voltage from the casing of the trans and the negative terminal of the battery, and there was about a 1000mV difference (about 1 volt), and after adding the ground wire, there was only about 24mV of difference), and it worked.....for a while. After driving around to test how it worked, it suddenly got about 10x worse than before, when it started violently knocking through the gears, and it happened at all speeds, to the point of me considering calling a tow truck, when I decided to shift to 2nd (because it wasn't responding to turning off overdrive (button on the side of the shifter)), and it stayed in second. After driving in second for a while, I wend back to drive and it started working right again for some reason.
also, when my parents took my car (because i took my dad's to work, and my sister took my mom's to work), they took my car, and it worked up until about an eigth mile away from our home, when it started to do it again.
Anybody know what could be wrong, and what I could do to fix it(if possible)? Since I am going to college, and would have trouble affording to have it fixed, advice would be greatly appreciated?
Also, whenever the temperature drops below freezing, the check engine light comes on, and it reports that the engine is running lean, anybody know what's going on there as well? | 
