Ford Fiesta MKIV 1.25 Zetec S - Master cylinder replaced now erratic idling!!

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Sun 21 Mar 2010 23:36
Ford Fiesta MKIV 1.25 Zetec S - Master cylinder replaced now erratic idling!! - Blimmer

hi all,

have done some serious searching on this site and many others an have yet to find a definitive answer!!

The story goes....

....This car belongs to my daughter and i am in the process of getting it ready for when she passes her test. Since she bought it she has had the handbrake/warning light on (even though she has only recently told me!!). So i went to check all the fluids etc. and found there was no brake fluid!!!! on further inspection it appeared to be leaking from the reservoir so, being on a tight budget, i replaced with master cylinder from a scrapyard. bled all the brakes and they now work fine, pedal is pretty hard but brakes come on well. The problem i now have is the engine will not idle properly and over revs!! When idling it fluctuates constantly between 900 and 1100 rpm. The engine runs fine when driving and sounds ok until you get to 3500 rpm (in any gear) where it starts to hesitate and struggle to get further (although it does occasionally). When you depress the clutch and roll to a stop at traffic lights etc. the revs climb to 3000, then drop slowly to 2000, then drop quickly to 1000 and go erratic again!?!?!?!?

i have read many posts with similar problems and have tried the following:

Disconnected MaF

Removed icV and cleaned

Disconnected Speed Sensor

checked all Spark Plug gaps and cleaned

checked all hoses

i am now at a loss!! one thing i forgot to mention was, when putting on new master cylinder i had the battery out completely overnight.

i have noticed that there is a gentle hissing sound around the servo when the engine is running but i cannot feel/see any leaks of air.

Thoughts and ideas are greatly appreciated as i am in a state of imminent hair loss

blimmer

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Mon 22 Mar 2010 09:02
Ford Fiesta MKiV 1.25 Zetec S - Master cylinder replaced now erratic idling!! - Robin the Technician

hi blimmer,

From the symptoms you describe the erratic idling can be directly attributed to the hissing sound. clearly there is a leak either at the servo or associated hoses. if you disturbed the hose or connector, then tese need to be thoroughly checked. You can use water around the joints - if its leaking then you will see bubbles. if there is a leakage in the sevo system this will upset the idling. as a test you could disconnect the servo hose from the engine, blank it off temporarily and the engine idle should be ok.

hope this helps

Robin the Technician

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Mon 22 Mar 2010 10:22
Ford Fiesta MKiV 1.25 Zetec S - Master cylinder replaced now erratic idling!! - Peter D

Second hand master cylinder is a false economy in my book. the clues are "pedal is pretty hard" and "hissing noise". You appear to have disconnect the servo vacuum home.

Regards Peter

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Mon 22 Mar 2010 10:56
Ford Fiesta MKiV 1.25 Zetec S - Master cylinder replaced now erratic idling!! - bathtub tom

>>if its leaking then you will see bubbles

are you sure? it's a vacuum.

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Mon 22 Mar 2010 15:32
Ford Fiesta MKiV 1.25 Zetec S - Master cylinder replaced now erratic idling!! - Blimmer

thanks Robin, will try this tonight and see what happens!!

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Mon 22 Mar 2010 19:51
Ford Fiesta MKiV 1.25 Zetec S - Master cylinder replaced now erratic idling!! - Blimmer

ok, so i took the pipe off the servo tonight and started the car. Waited for the choke to finish its work, revved the car and got the erratic idling. Put my finger over the hose and blocked it and the idle returned to normal!!!!!! every time i remove my finger a little the problem comes back!!! So now i know the hose is ok it must be the servo!! thanks Robin for your help, you are a lifesaver!!! Just got to source a new servo tomorrow, remove the cylinder and servo and replace, then bleed the system again, oh joy!!!!

i can only think that the old "bad" cylinder must have leaked into the servo and killed the seals causing a loss of vacuum.

Will post when i have replaced servo!!

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Mon 22 Mar 2010 21:25
Ford Fiesta MKiV 1.25 Zetec S - Master cylinder replaced now erratic idling!! - Blimmer

well, another turn up for the books!!!

the age old proverb is true, if in doubt check again as you have probably c@*cked it up!!!

was out tinkering again and had a look at the old master cylinder that i took off. Noticed there was a rubber washer around the part that fits into the servo, got me thinking!!! So, undid the bolts and eased the master cylinder forward slightly to have a look and lo and behold, No RUbbeR SeaL!!! Must have been left on the servo of the scrapper when i removed it!!! Slipped the seal off the old cylinder popped it on the new and did up the bolts. Started car, RUNS LiKe a DReaM!!!!!!!!! a simple rubber seal was my undoing!!! Just been for a test drive and all is sweet although i did have a little flat spot once or twice around 3500 revs so will look into a new coil pack too to be on the safe side but other than that it ran perfectly, always coming back to idle with no problems!!

all is good for daughter to hoPeFULLY pass her test tomorrow as she wants to come home and go out for a drive!!!

thanks all for the advice, got a few other things to sort which i will probably be posting about shortly but only cosmetic stuff!!

blimmer

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Mon 22 Mar 2010 22:30
Ford Fiesta MKiV 1.25 Zetec S - Master cylinder replaced now erratic idling!! - Robin the Technician

hi blimmer,

Glad to hear you got it sorted and thanks for keeping us up to date with your findings.

good luck to your Daughter on her test - it'll be all downhill from there......

Robin the technician

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Sat 13 Aug 2011 11:10
Ford Fiesta MKiV 1.25 Zetec S - Master cylinder replaced now erratic idling!! - josh+fiesta

hi i know this has been idle for a while but just need some advice, my 2001 ford fiesta zetec 1.25 has these EXACT symptoms, i was just wondering how something with the servo could affect the running of the engine and the revving in idle and in coasting ? but this has happened before in the last 5 months i had it repaired under warranty and didnt ask what was replaced, however it happened during rain, it has been relatively dry since but now the rain is back so are the problems? i am a very novice car DIY-er so easy advice would be much welcome

cheers josh

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Sun 14 Aug 2011 23:47
Ford Fiesta MKiV 1.25 Zetec S - Master cylinder replaced now erratic idling!! - Big John

A leaking servo seal would not be affected by rain.

For a misfiring fault in damp conditions I would start looking at the high tension ignition circuit i.e. coil pack , HT leads, or plugs

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