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Flat Spot In Low Revs, Mk4 Ford Fiesta! Driving Me Insane!!


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Hi im new to the forums so go easy on me haha but i have had this problem with mk4 fiesta 1.25 zetec! I have literally tried everything I can think of and still the same and ready to drive it off a cliff, but thought I should ask like minded ford lovers if anyone has the same problem!

I basically have a flatspot in low revs! you only reli notice it whens idleing, starting off or when your stopping and starting on the throttle when your in a traffic jam. But when you put just a small bit of throttle down the revs will shoot down instead of up and it will start juddering and spluttering and wanting to stall..sometimes it does! If you increase the revs to about 1500-2000 it clears the flat spot and its perfect then.

Have tried everything i can think of...first thought it was the TPS or idle valve so have replaced both of them along with a lot more but no result. Have had it plugged into 2 different diagnostic machines and no codes come up had it into 2 different mechanics and they cant figure it out! What i have noticed though is when its running if you unplug the TPS and plug it back in again it seems to reset the system or something and it runs almost perfect until you turn the car off again. So after i found that out i immediately reset the ecu thinking that might do it...but no nothing. So any suggestions what this might be?? Thanks!

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Check the crankcase breathers (hoses) PCV (positive crankcase ventilation) valve

I presume it is standard with a stock air filter etc and has been serviced recently with clean air filter, new correctly gapped plugs etc

Try cleaning all the sensor plugs/ sockets and disconnecting the MAF and drive it to see what happens

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Yh checked the PCV and hoses for any leaks and nothing! ran it without the MAF connected no difference. and yh brand new stock air filter and brand new spark plugs and HT leads, fuel rail, fuel pump, fuel filter, lambda sensor, idle valve, TPS. Cleaned every sensor that i havent replaced and checked and cleaned every electrical connection i can find and cleaned the throttle body completely! Im STUCK!

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