Punto uneven idle

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Thu 13 Feb 2003 08:09
Punto uneven idle - jonbenj
I've got a 1998 Fiat Punto 75 SX 1.2, multipoint fuel-injection and 34k miles. From time to time the idle speed starts to surge up and down, and the fuel injection warning lighr comes on, although generally speaking not at the same time. I don't have access to a code reader, but I'm guessing that it's the idle speed stepper motor. Plugs and filter are OK, and the system has had a good dose of Forte injection cleaner. Is there anything else I can do before I try taking the Idle control Valve out for cleanig (Don't fancy doing this cos the torx screws appear to be made of cheese!)

Thanks,
jonbenj
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Thu 13 Feb 2003 10:45
Punto uneven idle - Adam Going (Tune-Up)
Hi Jon,

Could well be a stepper motor fault, but cleaning is not always a cure. First I would check the Oxygen Sensor output, but this really requires a suitable oscilloscope. Once hot you should see the output switching between zero and 1.0v, peak to peak approx 15 times in a 20 second time span at idle. It is quite common to find it rising and falling VERY slowly, and the revs changing accordingly. You may also notice this if you try to hold the revs dead steady at about 2,000. If the Sensor switching gets slower and slower the longer the engine is at idle it may be that the Sensor heater feed or earth has failed. The four wires for the Sensor are:- battery voltage for the heater, earth for the heater, earth for the Sensor, and output from the Sensor.

HTH, Adam
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Fri 7 Mar 2003 20:31
Punto uneven idle - shaun wyatt
hi jonbenj
Had the same problem it was the fuel temp sensor.i think what happens is the temp sensor starts playing up and the ecu thinks the car is cold and sends more fuel to the injecters and so the car suddenly revs by itself.Hope you can understand what i am trying to say.Sensor was about £20 and is very easy to fit.
shaun
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