OK, my parents have a 92 tercel 2 door 4 cylinder 4 speed manual and 147,000 miles and for the last 2 weeks or so the check engine light has been on, It runs fine, but you can notice some power loss when you punch the gas,and when the car is warm, it has a very rough idle, you can hear a slight squeak from the engine and a sputter from the exhaust, we thought it was the oxygen sensor and we replaced it, and that wasnt it, and it has a brand new timing belt, does anyone know the problem?