Rough running engine - Diagnostic help

[ulfilias]

Hi There,

I had some plugs so I swapped the 4 on the missfiring bank and no difference at all, but it took me less than an hour so was worth the try.

I was going to take it to a local garage this afternoon and it wouldn't start. Turning her over gave backfires through the Air Intake ?!?!?!

Oddly she starts from cold no problems, and it had been 3-4 hours, but nope....I'm wondering what can cause that ???

Lee