Serious Power Loss *CAR*

[Martay]

Hi there,

My car is a 1997 Ford Fiesta 1.25L (MK4)

In short, it has developed a couple of faults that im confused about.

Firstly, it started over-revving during gear changes and 'high-idling'. This got worse to a stage where if the car was rolling above 5mph the revs would shoot up to ~3500rpm and not come back down until the car stopped rolling. It would also 'cruise control', sitting at whatever speed you left it at until you braked, or de-clutched.
The various ford forums suggested a faulty sensor, and said to unplug the vehicle speed sensor (VSS)
This cured the over reving.
The car now has developed a 'no power' problem. From stone cold the engine is fine, normal power, acceleration etc. When warmed up, there is no power, and the car struggles to hit 60, coughs and splutters at all revs, and dies at idle if the throttle is blipped.
Because of this, i have replaced the throttle position sensor, idle control valve, intake temperature sensor and MAF (air flow sensor).
None of the above have solved the problem. I have stripped most of the intake and cleaned with carb/injector cleaner.
Im totally baffelled by this, and so are the ford forums, and im sick of the fuel bill from driving it foot-flat constantly, so any advice greatly recieved
Ta
____________________
Eat well, poo hard
Drives: Cavalier 2.0 16v
Rides: Slightly ratted Honda City Express

[reggie]

stuck on choke ?or whaterver fuel injection uses
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when the shit hits the fan make sure its facing the other way.

[ZRX61]

Blocked exhaust?

[Phoenix]

You may have just forgotten to put it in your post but based on the fact you unplugged the VSS and it cured the over revving but created the power loss problem, would it not be a simple case of buying a replacement VSS that works rather than leaving it unplugged.

[stevo as b4]

Have you checked the ignition system and the base timing setting? The ECU will control the ignition map over the rev range, but if the base or idle timing is not correct then it could all be out completely.

You have replaced most of the engine sensors, but have you checked the coolant temp sensor, and also the crank sensor. The latter normally works or it doesn't though. Also you could have a faulty thermostat or a stuck open stat that's causing the poor mpg and fast idle when warm. this has happened on 2 older car's i have owned.

Lastly have you had the car's ECU interrogated for fault codes? This does'nt have to be done by a ford dealer, anyone with the diagnostic software on a lap top with an interface and cable that plugs into the OBD port can check for fault codes. I would also as an outside measure do a compression test, but i don't think that this is the issue really. It must be fuel or electronics related somewhere.

[0l0dom0l0]

what about the air fuel ration sensor inthe exhaust? have you changed that. from memory they are only activated when the egnine is warm, so it fits with your cold starting running fine scenario.

[Martay]

Thanks for the responses.
Just a little update, i stripped and cleaned out the throttle body and intake yesterday. Was pretty mucky but didnt cure the problem though. Was more a learrning curve for me!

Phoenix - yes, sorry, i have replaced the VSS.

stevo as b4 - Im unsure of how to check the timing settings. The car is currently in at a little independant auto-sparks to get the fault codes read/reset/test driven etc. I have not yet checked the coolant temp sensor or crank sensor, to be honest, they didnt cross my mind! If the auto-spark cant find the problem, they'll be my next port of call.

0l0dom0l0 - Is this also known as Lambda (sp?) sensor, in the manifold? If so, as above, thats where il be checking next.

Many thanks guys, really appreciated
____________________
Eat well, poo hard
Drives: Cavalier 2.0 16v
Rides: Slightly ratted Honda City Express