Ford fiesta zetec idle problems?

hi im chris i own a 98 1.25 zetec. I fitted a new idle control valve to it but the engine doesnt idle . after ten or fifteen minutes when its warmed up the revs drop to almost stalling point then go back up and continues to do this for a while . then after a while the car idles fine then it will do the idle dipping again any ideas would be appreciated ??

Answers:
sounds like lambda(o2)sensor to me you can check resistance on sensor,you will have to get resistance parameters from somebody. If your a bit more experienced check voltage from sensor(it should fluctuate between 0.1v and 0.9v).. You could also check sensor wiring connections but that's about it ..If you have problem doing this then take it to a mechanic with a diagnostic scanner to sort out problem .good luck..
Had my Fiesta for six and a half years and she never idles or stalls. course, now I've opened my mouth.:-(
Maybe the software of the Engine Management Unit needs readjusting to compensate for the new idle control valve (which I assume is fitted correctly!). Take your car to a Ford agent and ask them to carry out a computerised check. If all is OK then at least you would know it is a mechanical rather than a software problem. NB I had access to a Fiesta 1.25 LX and that had a similar problem; tweeking the software settings sorted it out, so it is worth a try.
Sounds like the baseline idle is set too low adjust the screw so get it to normal temperature and just increases the idle a tiny bit say 50 rpm back it off just a few degrees and this should cure it,
could be lamda senser but get it to ford as there are meny senser on that car that could go rong

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