Ford Fiesta 58Reg Malfunction I.e. Lack Of Power

[NONREV]

I have taken my Fiesta three times to a reputable local long established family garage who are unable to diagnose the problem even with computers and diagnostic equipment. The problem is that I can only get up to 10 mph with a stuttering and lurching some what like a learner driver slipping the clutch,also the foot brake pedal becomes very hard to depress when the car is in motion. With the malfunction light on the engine will still run with very little power and so is unable to be driven

[bhg481]

Since the power-assistance for the brakes relies on the vacuum in the inlet manifold and you appear to be lacking power-assistance, together with the lumpy running, it implies to me that you have a leak in the inlet manifold. This can be anything from a bad gasket to a crack in the manifold.
You may be able to hear a sucking noise from the manifold if you listen carefully. I seem to remember there was an old trick of using an unlit butane torch to blow gas around the inlet; if the engine note changed it showed there was a leak as the gas was sucked into the engine instead of air. Perhaps someone else will confirm/deny this memory.

[TWR]

I agree with Bhg, also check the pipe coming out of the Servo.

[bhg481]

That's probably the most likely TWR, and the cheapest repair.

[Hymie]

It could very well be an issue with a leak somewhere around the intake manifold.

Although I have not heard of using butane to confirm the leak – I once had an intake leak around the base of a carburettor (due to a garage throwing away the gasket); this was demonstrated to me by a mechanic spraying WD40 around the base of the carburettor, resulting in an increase in engine idle speed. This method might be safer than using a bottle of butane.

Another possibility is fuel starvation – I once suffered very similar effects on a vehicle, which after much investigation was found to be due to a blocked fuel filter in the fuel tank.
The fuel filter was not mentioned in the full workshop manual for the vehicle – it was a colleague who had suffered exactly the same fault with his car who advised me of its presence.