Ford Fiesta 97

I have a problem and I want to know if someone can help me,
I have a Ford Fiest 97 Endura 1.3 to NAFTA. It is the Spanish model.
The problem I have is that when I walk and under the speed I stop, they told me that it can be the step by step. But they already cleaned me and the problem persists ..

What can I do?

thank you so much

Indeed, it can be the step by step, but it is good when a cleaning is performed to this component, also perform it to the admission body to be sure that the air passes correctly, sometimes it is not enough only with the step by step, test and luck.