2009 Ford Fiesta ignition coil

I dont know why you had to replace the ignition coil in the first place , was it faulty ? Ignition lead/s are usually more common to fail than the coil and causing misfire , running rough .

when they where diagnosing the car it was showing oxygen sensor and coil ignition , so the mechanic told me to replace it . I did replace both and the light was gone for few days and came back again and when am driving it sometimes looses power or shakes a bit .

When were the spark plugs last changed ? As Whittingham has advised ignition leads would be the first call after spark plugs.

If the light is back on there should be a stored fault code that will show when scanned . Impossible to really give you a definitive answer from here , could be a plug lead breaking down under load , plugs needing replaced , MAF needing cleaned / replaced .

Thank you very much I will have to check the ignition lead because I don't think it's the spark plugs , I have serviced a car first week of November .

If there are no visible signs of the plug leads being faulty you need to check with a multimeter (or ohmmeter) to see if they are in specs .

I will do that thank you.

1 more question what will be the cause that makes spark plugs to crack ?

If the porcelain is cracked the most common reason is fitting incorrectly or with the wrong plug socket . If cracked , they usually short and cause misfire , lack of power .