try these 3 things just before you get it tested,
1st always change the oil before you get a car tested, because it will have a certain amount of gas contamination in it and will cause your cars to fail at times.
2nd either change the air filter or take it out (just for the test) that way it sucking in cleaner air.
3rd. this is a cheater but remove the PCV and just lay it on the valve cover BUT still attached to the vacuum line, this also will let your car suck in cleaner air.
i did these thing on my 84 burb because it had failed BADLY, & by doing these thing it passed w/flying colors..........joe