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Car in question is a 1998 1.1 Saxo with single point Bosch injection. When ticking over it revs very low despite the stepper plunger moving. If cold I have to touch the throttle to stop it stalling. At random when driving the speed will suddenly decrease by about 15miles an hour then return back to previous speed in a pulsing fashion. I have changed ,plugs,leads,lambda probe,fuelfilter,coil, temp sensor (to ecu), exhaust and cat were change about 2 months ago. I drained out some petrol for a contamination check. All contacts have been cleaned. All pipes checked for leaks. When I took the plugs out they were sooty. I wonder now if fuel delivery pressure is ok but not really sure if i can check this very accurately. Help !!!!!!!
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Classic symptom of a failing throttle potentiometer. Not available as a spare part, only as part of complete throttle body. Contact in nose of stepper motor could also play a part but failure tends to make the idle speed go high. Rather than a new throttle body, try a scrapyard. Remember the Saxo is the same as a 106 peugeot to widen your search.
Andrew
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Simplicate and add lightness!!
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popped the plugs out again. Once again sooty, would the potentiometer affect the mixture? I should add fault light is not illuminated. Is it possible that a fault would /could be logged without the light being illuminated? Thanks for giving me a new direction. Unable to get car to dealer till end of next week, so I am quite happy to play when I get a few minutes spare, until then. I don,t think I mentioned the car has done 29000 miles.
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Not all faults will flag the MIL light but will be logged all the same. On a couple of occasions where the pot has been 'adjusted' overfuelling has resulted. Coolant temp sensor could be a problem if it has 'locked' within its operating perameters then the ECU would see nothing amiss yet the fuelling would be correspondingly locked with little activity from the O2 sensor. In a situation like this I would read the ECU for codes then clear them then start checking the serial data looking at idle position, coolant temp, voltage at ECU, output from throttle pot and throttle (idle)switch, O2 sensor activity etc then go from there, pinpoint checking anything untoward.Worth checking the coolant level, if it is low enough to uncover the temp sensor that will upset things.
Andrew
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Simplicate and add lightness!!
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Through my ignorance I dismissed the potentiometer because I totally overlooked the fact that this car does not moniter air flow/mass. I assumed that any fluctuation from the potentiometer would have the mixture compensated for by monitering of the air. I have not had a chance to get back to the car but as you say everything does point to this unit. I thank you once again for pointing me in this direction.
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Started car today, stationary or moving the revs just kept pulsing at a regular rate. I pulled the 5amp fuse supply to the ECU (hoping to capture just this fault code). Car restarted no problem and after five minutes the fault had not returned. Is it possible that the original fault(coil?) could have corrupted the ECU and that by not checking/clearing any fault codes that may have been logged this caused the running conditions I have been experiencing? at the moment I do not have the confidence to try the car out tonite before I go to work.
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Effectively you have rebooted the ECU and wiped its adaptive memory. It is possible that there may have been a glitch in the system causing the problem within the ECU and by rebooting it the system will now function correctly, for a time at least, just like the home PC = Alt,Control,Delete!!!
Keep us posted
Andrew
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Simplicate and add lightness!!
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This week is proving to be a bit of a learning curve for me. I was misinformed about the use of the 5amp fuse I pulled. When I checked against the wiring diagram I could see it was the Lambda probe so it must have been a coincidence. The car continued to run perfectly until I stopped for fuel after ten miles then the problem reappeared. I plugged in a gunsons fault code reader to the green (diagnostic?) socket near the battery and it was totally dead (code reader ) so I guess the only access point is the one in the car fuse box. For which no socket was supplied. I have now disconnected the battery for 2mins and the car is now driving perfectly although I imagine this is just a coincidence. Once again I do not have time to give it a thorough try out. Having read the article about the cost of a throttle potentiometer for the peugeot 106 I was absolutely amazed at the cost. Still happy to keep playing till the end of the week. Thanks for your input.
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Stepper motor replaced . Fault has not reappeared in 100miles. £128 + VAT trade at main dealer. £120 + atEuro car parts. £65 + Vat at GSF Car parts genuine Bosch part. I have no connection With any of these, but I feel GSF deserve a mention. I am still mystified as to how a stepper motor (high resistance) can cause a problem when the throttle is off the stop (assume plunger parked in wrong position must tell ECU that the mixture needs adjusting?). THE END
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