2003 ford focus standard, losing power.no problem changing into gears.what can I look at first?

2003 ford focus standard, losing power. No problem changing into gears. What can I look at first?

Possible catalytic convertor clogging up. Run engine and check tail-pipe for excessive blow, cover your hand over pipe end to check that if engine idle suffercates.

Try a fuel additive to clean the injectors. Most of the time the require a full tank of gas then you add a full bottle, fill it with the highest octane cause it will burn better. Just read the instructions on the bottle.