Punto Mk2 16v: engine cutouts while idling?

Hi,
my Punto Mk2 ( 16v ) shows an annoying behavior. While idling the engine has random and frequent cutouts, i.e. a cylinder isn't fired. This leads to a mildly shaking car and a not very
healthy sounding engine, especially when the engine is warmed up. While driving I don't notice any cutouts.
My authorized garage wasn't very helpful. They said that the computer diagnostics doesn't show any problems and they have to replace some expensive parts trial and error to locate the problem ( throttle valve or electronic control unit ). It's obvious why I'm not very happy paying around EUR 500.- for such a proceeding.
Are there any known issues with this engine that could cause the problem? At least it should be clear if the problem is connected to the fuel injection or the ignition. I suppose that not fired petrol could cause some damage to the catalytic converter. But the exhaust emissions doesn't smell of patrol ...
I plan to switch to an independant garage which may has some more motivation to locate the real error, not just exchanging whole units. What should they check? Any hints?
Thanks in advance!
Bye, Jan
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Jan-Sebastian Winckelmann
Henstedt-Ulzburg, Germany
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On 19-Apr-2004, Jan-Sebastian Winckelmann

As it happens when idling during tickover I suggest you get one of the little neon ignition testers that goes on top of a plug, in series with the ignition lead, these are good for showing no spark. In practice, as they are difficult to use in daylight, I use a timing light in series with the coil. Of course this falls down if you have a badly carbonised plug that is bridging out and not firing. Other than that proviso, if the light flashes while the engine misses it is unlikely to be a vibration induced electrical intermittent or a bad coil.
I have met a Fiat with a short length of hose buried behind the engine between the fuel pipe from the tank, and the fuel filter which was on a bracket. It had a split, and at low revs the fuel pump was pulling mostly air, at higher revs it ran ok.
Intermittents are always a challenge needing methodical deduction, and don't forget Fiats are not noted for good electrical grounds.
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ato snipped-for-privacy@hotmail.com wrote in

Thanks for your advice. My independant garage was able to locate the problem. It was a faulty spark plug, not easy to find. The spark plug looks almost o.k. but the isolator looks brownish where the metal part of the plug starts, there are also very tiny pieces of melted metal visible. The sparks must have choosen a strange path. My authorized garage still is convinced that their computer should have been able to locate this problem.
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Jan-Sebastian Winckelmann
Henstedt-Ulzburg, Germany
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