suddenly lost power. No acceleration and can't seem to get over 50 mph

What is your question?

My daughters car is a 99 chevy cavalier. We bought it about 3 months ago it has run great until yesterday. The reason they were selling it is because it wouldn't pass emissions and we aren't in a county that requires emissions. It has the in-line 4 cylinder engine and automatic tranny. Its a combination CNG unleaded gas car but has had the CNG disconnected. I've put some marvel mystery oil in the fuel tank and checked the air filter.

How long has your 1999 Chevrolet Cavalier had this problem?

2 days now