I have a 2012 Toyota Camry with 171,000 miles on it and every time the eco light is not on the car drives like a stick. it drives like somebody first learning how to drive a stick. it also gives a harsh vibration at certain speeds.
The harsh vibration is probably the torque converter shudder that these cars develop because of a faulty torque converter design. The other condition you describe may be the transmission starting to fail.
Start with the easy stuff: Eco mode comes on when there's reduced demand for fuel. When it's off, perhaps the engine is not getting enough fuel. The tranny strains, etc.
Start with these things:
1. Clean the MAF sensor and the throttle body (Fast, Easy and Cheap to do);
2. Replace your engine air filter;
3. Check your fuel filter. At 171K, it might be clogged, or perhaps there's a restriction in the fuel line.
4. Check your spark plugs;
5. Check your O2 sensors.
It may not be the transmission, at all. Or, more to the point, the transmission is the symptom. Since these issues come on when more fuel/power is necessary, it could well be related to any and all of the above.
If you have a Blue Driver or some other scanner with enhanced data/live data capabilities, use it. Getting a peek at that data would be useful.
