This could be an airleak after the airflow meter, any expose dragged in here isn t seen by the ECU and hence not compensated for and can thin the engine out and can then permit the engine to rev going on in the same way as not desired causing aggressive running. As its a mechanical aberration it tends not to slant upon the idiosyncrasy fresh and you can sometimes listen a hissing noise as soon as 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 swine delivered to the engine. Might along with be worth cleaning out the idle speed control motor / valve as these get clogged in the works once carbon and some brake cleaner washed through helps clear things off.
in the manner of I start the car, the engine surges up together with 1200 and 2000 rpm help and forth. I changed the IAC and the TPS next no bend in symptoms. I have noticed that several Lexus SC's have this thesame issue. Prior to this I would have to adapt the idle promptness screw to subjugate the rpm and it would preserve for a while. Now, the engine is constantly surging to the dwindling where I cannot steer it for apprehension of broken to the drive train. Any experienced solution?