white smoke can be caused in several ways. If you aren't losing oil and theres no smell from the smoke then that discounts oil. That leaves air/fuel ratio which would be indicated by high consumption and low power (is the car choking constantly?) and the other one is coolant burn if theres a crack or a gasket leak burning coolant will produce white smoke as well. Are you topping up the rad alot or losing coolant at all?
Hopefully its not the coolant one in which case i'd look at the MAF and the lambdas to see if they were functioning correctly. Have you taken it to have the codes read from the OBD might save alot of time
'HIgh consumption/low' power is correct - the rad is not losing any coolant - that leaves the MAF and the lambdas but what are these??? And what's the OBD? As you can tell I am not too literate in these terms - thank you for you help, further assistance would be great, thanks.
THe MAF sensor is a little black sensor that sits on the intake just behind the air filter box/assembly it measures mass air flow and temperature of the intake it thats not functioning correctly that will throw the fuelling out. The lambda sensors are a set of probes that sit in the exhaust on and behind the manifold and measure the o2 content of the exhaust gasses, a lambda failure would probably have more effect than the maf tbh. OBD is the on board diagnostics if you take the car into lexus/toyota they will be able to read the codes from it and might be able to tell you straight away whats failed.
I'd suggest going to get the codes read first then if needs be do the replacements, lambda sensors can be gotten fairly cheaply but a MAF or piece of electrickery may sting you