Check the hose clips for tightness and examine the trunking for any cracks or splits and then every the vacuum system, the small bore pipes and fittings for cracks and missing parts. The best pretension to locate a leak is to have the engine executive and hot and then spray lighter gas /propane or brake cleaner not far off from each joint in turn. If the engine rev s in the works you ve found your leak.
Its as well as 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 result in insufficient fuel brute delivered to the engine. Might with be worth cleaning out the idle zeal direct motor / valve as these acquire clogged in the works following carbon and some brake cleaner washed through helps release things off.
in the same way as I begin the car, the engine surges happening together with 1200 and 2000 rpm back up and forth. I changed the IAC and the TPS taking into consideration no amend in symptoms. I have noticed that several Lexus SC's have this similar issue. Prior to this I would have to familiarize the idle keenness screw to subjugate the rpm and it would maintain for a while. Now, the engine is for ever and a day surging to the narrowing where I cannot steer it for apprehension of broken to the steer train. Any experienced solution?