Erratic RPM at idle.

[pascaltissot]

Hi , I have a Range Rover 1998 ,4.6 HSE in very good condition it has only 42,000 kilometers ,I am experiencing a problem that is driving me nuts ….in low rpm the car has an erratic idle regime , you feel it in going up and dawn in stops ,the differences in RPM is not much but you feel it inside the car .I know this car since new and this new episodes took me to change the plugs , the step motor ,the cold starting resistance ,etc .I have a Autologic computer , and I checked and there is no faults in the system .Just in case I checked the battery ,but since it is new, no news there .The last thing to do I think is to take apart the plenum chamber and check if any air intake somewhere or leaks ??do you have any ideas on were to look ??
Thanks for your advice
Pascal.

 

[joey]

You changed the step motor that would have been my first thought, have you ran any injector cleaner through it just in case something is just dirty? How about the TPS (throttle position switch), clean the MAF sensor.

Fuel Filter (has it been replaced?)

 

[pascaltissot]

Joey, yes I did clean the injector two cans of cleaner ,engine on and gas pump out of coarse , The TPS was change also because I thought it might be there two but not .I change the temperature sensor in the air filter also .air filter is new .No strange noise in engine everything normal, no noise not even when cold ,no valves noise .cleaned the sensors all around but still erratic 625/650 rpm up and dawn ….at idle .
Saludos

Pascal.

 

[pascaltissot]

Yes fuel filter is new .sorry
Pascal.