I googled it and came up with this response in a discussion thread. (taken from
http://www.medhelp.org/posts/Allergy/I-smell-exhaust-fumes-all-the-time/show/1245562)
"Hi, smelling exhaust fumes or such strange smell can be present in certain conditions and it is termed as Parosmia (abhorrent odor perception).
It is usually associated with rhinosinusitis, head trauma, viral infection, or oral problems.
It frequently disappears with successful treatment of the above mentioned conditions.
Apart from treatment of the cause or in conditions wherein the cause remains unknown, in such conditions Anti seizure or anti epileptic medication like clonazepam against prescription is sometimes helpful esp. in persistent cases.
You can use scented wax or incense sticks before sleeping. You also need to maintain good sleep hygiene.
I suggest you to consult ENT specialist to rule out the cause. Take care and regards. "