This could be an airleak after the airflow meter, any let breathe dragged in here isn t seen by the ECU and so not compensated for and can lean the engine out and can then allow the engine to rev going on once not desired causing coarse running. As its a mechanical irregularity it tends not to viewpoint upon the idiosyncrasy well-ventilated and you can sometimes listen a hissing noise when the engine running.
Its then worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a not at your best pump will every outcome in insufficient fuel physical delivered to the engine. Might also be worth cleaning out the idle promptness direct motor / valve as these acquire clogged going on bearing in mind carbon and some brake cleaner washed through helps forgive things off.
as soon as I start the car, the engine surges happening amongst 1200 and 2000 rpm put up to and forth. I untouched the IAC and the TPS considering no tweak in symptoms. I have noticed that several Lexus SC's have this similar issue. Prior to this I would have to familiarize the idle swiftness screw to subjugate the rpm and it would maintain for a while. Now, the engine is continuously surging to the lessening where I cannot drive it for siren of damage to the drive train. Any experienced solution?