90 caravan 3.3 litre loss of power

[gro]

Hi everyone. New here and hoping for a answer or at least a clue. My van on occasion will lose power and appear to backfire through the air cleaner. It is not always from a stop and does not occur during winter months. If you pull over and put it in park or neutral it will rev no problem but under load it will act up. After the burping is finished either by sitting or cooling off or just pumping the gas it is fine - until the next time which could be 5 min, - 5 hrs. or a couple of days. It has been in the shop and the computer shows nothing. It's really ticking me off. Thanks for any suggestions or help.

[Taz480]

Replace the plug wires.

...and of course the plugs, too, if it's been a while.