Fiesta 1.25 LX - Odd idle, RPM surge on gear change, misfire: help?

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Wed 18 Feb 2015 18:11
Fiesta 1.25 LX - Odd idle, RPM surge on gear change, misfire: help? - MeMikeyou?

So I have a 1.25 zetec se engined Fiesta with around 64k miles (2002!) Since I bought it, it has been plagued with an inconsistant misfire at all RPM but most noticeable under acceleration/higher (+50mph) speed. I say inconsistant; It doesn't feel like it's missing on one cylinder alone, or that it's missing on the same cylinder all the time.

A quickndirty trawl around the net and I changed the coil pack which has improved but not eliminated the problem however:

Now, during gear changes the revs rise to 2500+rpm before returning to 'idle'. If driven very gently, throttle lift-off reveals the same effect - I can feel it 'autocruising' for a moment before the speed begins to fall.

It idles at around 1100 rpm, but if I give the throttle a prod, the idle begins to surge between 1000 and about 1900 or so RPM on a continuous cycle until EITHER, I drive off whereby all is again fine at the next stop and idle, OR I turn the engine off and restart.

This isn't a direct result of the coil pack change, it developed some weeks later. I've put some Redex through it with no discerable improvement.

I've just got hold of a OBD scanner and 'Torque' app, but I don't know how to configure it, and there are no fault codes stored or check engine light.

Any clues? Advice on the torque app would be greatly appreciated too

Thanks in advance, and apologies for the length of my first post.

Mike

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Wed 18 Feb 2015 19:06
Fiesta 1.25 LX - Odd idle, RPM surge on gear change, misfire: help? - Oli33

Only changed the coil pack? What about the spark plugs?

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Wed 18 Feb 2015 19:22
Fiesta 1.25 LX - Odd idle, RPM surge on gear change, misfire: help? - MeMikeyou?

Not yet, nor the HT leads. Car was sold as serviced (it does have new timing belt and filters), I know I shouldn't make assumptions about what constitutes a service, but having presumably wasted my time and money on the coilpack, I thought I'd ask before throwing any more money at the problem, especially as it seems (to me) to be ecu related.

Mike

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Wed 18 Feb 2015 19:44
Fiesta 1.25 LX - Odd idle, RPM surge on gear change, misfire: help? - KenC

I read somewhere that disconnecting the battery will allow the ecu to reset itself, if you have the radio code its worth a try and will not cost, also give the terminals a clean up at same time.

Also this previous post maybe worth a read

www.honestjohn.co.uk/forum/post/index.htm?t=36472

Edited by KenC on 18/02/2015 at 19:53

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Wed 18 Feb 2015 20:07
Fiesta 1.25 LX - Odd idle, RPM surge on gear change, misfire: help? - MeMikeyou?

Thanks KenC, I also read that post before posting:). I tried the disconnect the battery thing a couple days ago. No joy :(

The thing is, I'm perfectly happy to start tearing the thing apart but the thing I'm lacking is some kind of 'process tree'. Since the introduction of electronic engine management everything depends on everything else and it's difficult to know where to start which is why I got the Torque app (which I have yet to figure out). Oh for a X-flow and a pair of '40s...

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Wed 18 Feb 2015 22:24
Fiesta 1.25 LX - Odd idle, RPM surge on gear change, misfire: help? - Railroad.
Check the vacuum hoses underneath the inlet manifold. Perished or split hoses are very common, and if they are then replace them.
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Sat 21 Mar 2015 09:15
SOLVED: Fiesta 1.25 LX - Odd idle, RPM surge on gear change, misfire: help? - MeMikeyou?

Sorry for the lateness of the reply.

Spot on Railroad: A split in the vacuum pipe as described. I've replaced it and all is now fabulous - ALL the problems (incuding the slight misfire) are now solved.

For the benefit of others who may read this while trying to fix similar problems:

There are FIVE vacuum take-offs on the 1.25 Zetec SE engine inlet manifold (Air-cleaner on top of the inlet manifold). Two are underneath, interconnected by a hose, and can be most easily found by following the run of the PCV hose on the left side of the inlet manifold (as seen from the front of the car). Two are located beneath and on the left of the throttle body and are for respectively, the brake-servo vacuum hose and the carbon cannister purge valve, this latter using a soft rubber similar to the PCV hose and also subject to perishing. Finally there is a vacuum hose which goes from the bottom of the fuel pressure regulator to the back of the inlet manifold and again is subject to the possibilty of perishing - mine was so loose at the manifold end it came off just by looking at it. Needless to say I've replaced it also.

Edited by MeMikeyou? on 21/03/2015 at 09:19

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Sun 22 Mar 2015 10:30
SOLVED: Fiesta 1.25 LX - Odd idle, RPM surge on gear change, misfire: help? - KenC

Hi Mike, glad to hear the you have found the problem,I have an interest because a relative owns an old fiesta with the same engine.

I wonder prior to replacing the vacuum pipes were you suffering poor (high) fuel consumption as one of your symptoms ?

Also do you recall the diameter/size of the replacement vac-pipe and the source from where you purchased it ?

thank you ken

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