i have the same prob with my car...
it's been crawling with loads of cockcroaches...
what i do was i sprayed almost every part of my car using ridsect..
every part i meant was every place that a cockroach can hide,but i never sprayed it at the engine part...
after i finish spraying all the ridsect, i closed all doors and windows...
the next day my car is roach free...