Driving on the highway a smell similar to onions or butane gas wafts into cabin on 2004 Toyota Land Cruiser

vehicle has done 180000 Kms has been serviced every 10000 since new.There are no oil leaks. This problem has been noticed over the last 50000 Kms. It is a petrol engine

Asked by for the 2004 Toyota Land Cruiser
ck exhaust system may have a plastic bag burn't to it. iv seen this several times and the smell is very bad like you say