What causes a car to misfire? on 2002 Ford Focus

Car started misfiring, replaced the maximum air flow sensor. Car ran normal for 2 days and has started misfiring again, could the sensor be defective or is there something else that could have caused this? Also, car has had an intermittent issue of stalling when I coast to a stop, it's a 5 speed manual tran. Just seems to idle weak at times, could these issues be related?

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2 answers 3 comments
basics. look at plugs. when was the last time it was serviced??

look for pcv line to have a hole in it by the 90 degree bend at the throttle body.

Roy
Hi Roy~
Had new battery, plugs and serpentine belt installed in June. I'll mention pcv line to my mechanic. Thanks!
Check (NOT REPLACE) Idle air control valve. Pull plugs and keep them in order of cyl. they came out of.Was it you or a shop that replaced the mass air flow meter?Was air FILTER replaced at same time as M.A.F.?...If not - some debris may have gotten up into sensor causing a faulty reading. Let us know.
Hi Ziptie~
My mechanic replaced sensor. I used to do oil changes, change plugs and brakes on my '91 grand am, but now I leave it to the pros, don't want to create other issues. :) Air filter has not been replaced and have been considering a K&N filter which I'll do this week.
STICK WITH O.E. AIR FILTER JUST REPLACE IT AS NEEDED. WAS MAF SENSOR REMAN?
IF SO THEY GIVE SOME TROUBLE. CHECK ENG. LIGHT ON? HAVE MECH. SCAN AND CHECK
IF SYSTEM GOOING OPEN LOOP,MAF CAN BE YOUR PROBLEM STILL,ALONG WITH OTHER
ANSWWES.JUST FIXED ONE, SOUNDS LIKE SAME DEAL.