I have 93 Lexus ES300, too. I have similar problems: white smoke, gas-smell, high RPM in low gear, really bad gas consumption. I am also wondering if changing ECM can fix these. Thanks.
It certainly fixed all of the problems I was having. I litterally had raw gasoline coming from my tailpipe, terrible gas cosumption (obviously), white smoke, etc... After I had the garage put the new ECM in, all of those problems are gone! I suppose I could have gotten a cheaper ECM elsewhere and replaced it myself but I really had no idea what I was doing BUT after seeing what was done and now knowing the "how to", I could definitely do it myself. I would try ebay or elsewhere for a rebuilt ECM if I were you. It would also be a good idea (in my opinion) to just DIY. Much less expensive and come to find out, it's probably not all that hard if you have a repair manual.
Hi I have a 94 es300 I had the same problem.The smoking gas smell and so on. I had it fixed last week. It also was the ECM.