Thursday,22-December-2016
Xantia: XU7JP4 - SL96 1.8 idle problem [fix]
EN
Problem:
- the car suddenly when stay somewhere at idle start rising to over 1200,or lowing below 800 the RPM`s with no reason
- most of that happen only when engine is warm
- the error what ECU log was: “mixture top position”. That registered with LEXIA
Solution:
- all troubles was from the VDO-MARELLI idle motor.
What was checked:
- both plastic “nozzle” near the idle motor. Their O-rings has been replaced with new. No issue - problem stay
- checked the canister and oil pipes connected to the upper “nozzles”. No issue - problem stay
- little lazy O2 sensor, was replaced about 25 000km. Signal average. Problem stay
- TPS sensor check - good signal. Problem stay.
- on hot engine and idle start messing the rpm`s, only unplug the idle motor connector immediately make the idle stable.
Seems with years gone, the motor gear that move the shaft-valve get wear and the correct position is not achieved.
For example, the ECU set 25-30 steps and expect after that rpm to be 850-860. O2-sensor must return between that and that value but in fact it come different. Then ECU lean or rich the mixture but the rpm goes wrong, and same with the lambda signal. The ECU move little the idle motor few steps but because the mechanical backlash it move too much or too less. That bring constant loop. So, if you get into that problem try to unplug the connector and see how it goes.
And why not get into trouble when is cold? Well, then same as accelerating the O2-sensor back signal is ignored.The ECU do not care what come as data until the right point.
