This could be an airleak after the airflow meter, any let breathe dragged in here isn t seen by the ECU and thus not compensated for and can thin the engine out and can in addition to allow the engine to rev going on once not desired causing rude running. As its a mechanical idiosyncrasy it tends not to slant on the irregularity well-ventilated and you can sometimes listen a hissing noise taking into consideration the engine running.
Its plus worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all consequences in insufficient fuel being delivered to the engine. Might also be worth cleaning out the idle rapidity rule motor / valve as these acquire clogged stirring in the manner of carbon and some brake cleaner washed through helps pardon things off.
in the manner of I begin the car, the engine surges up in the company of 1200 and 2000 rpm back up and forth. I untouched the IAC and the TPS in imitation of no correct in symptoms. I have noticed that several Lexus SC's have this same issue. Prior to this I would have to accustom yourself the idle speed screw to demean the rpm and it would withhold for a while. Now, the engine is until the end of time surging to the dwindling where I cannot steer it for radio alarm of damage to the drive train. Any experienced solution?