The clean air filter is behind the glove box. Simple to get at - open the glove box and feel around for the hinges at the bottom. Push out the plastic 'pins' from the hinges and the whole box comes off. Behind is a black plastic box with a cover that just pulls off, and the filter is behind that. It will just slide out and you may be surprise how much rubbish is stuck to it. I cleaned mine last week, and despite it being supposedly changed at the last service it was black and full of insects, seeds etc. I suspect it wasn't touched during the service. I would have thought it unlikely for the smell to come from that though - unless theres something more nasty stuck to it!! I used one of the gas bombs before and it was good - Lexus dealers seem to have a few knocking around that you can buy.
Good luck!