on acceleration car will not go over 20 miles per hour and engine revs up and down

Here is a walk through diagnostic for your su=ituation. Just follow the links below;

https://www.2carpros.com/articles/engine-surges

check timing. your car is in limp mode or aka safe mode and my car was in the same thing and mechanic checked timing and it was off a little. also other reasons could be airflow. something with exhaust, vacuum, or intake one of the those or more than likely the reason for safe mode. safe mode is when your computer senses something isnt right and it wont let you blow up your motor

You could have a clog in the intake or exhaust. Sometimes the catalytic converters fail and fall in on themsleves. You can do a quick check, this is not fir sure it is bad, by smacking ti with a rubber amllet or your hand and listening for loosee material. Remember you have more than one in some applications.
A large vacuum leak would also cause this behaviour and it should be something you can hear with the engine running and the hood open.