The family of a mother and her three children found dead in their Ashburton home are waiting for their bodies to be returned before finalising funeral arrangements.

Bishop Moea Pongia, of the Church of Latter Day Saints is communicating with the parents of 31-year-old Cindy George.

They're currently in Rarotonga, waiting for their flight to New Zealand.

Bishop Pongia says they've asked for only friends and family to attend the funeral.

Meanwhile, experts are struggling to piece together why an Ashburton family tragically left a car ticking over in the garage.

Cindy George and her three small children were found dead in a Thomson Street property last week.

Police believe the family was accidentally gassed by a running car, but full autopsy results are expected back this week.

National Poisons Centre toxicologist Dr Leo Schep said it is difficult to know if the family could smell the gas.

He believes that when toxicity occurs, other people may notice but you may not be aware yourself that you have it.

"You may get a bit of headache and a bit of nausea...you'd also get confusion, poor concentration and your ability to make judgement calls can be compromised when you start getting serious toxicity."