I have an o2 chrysler voyager. Going down the road it surges and especially when slowing down. It doesnt do it all the time. Of course when I take it to a repair shop, it runs fine. They have driven it for a couple of hundred miles and they say it runs fine. All the time they have a scanner hooked up and no codes pop up. Any suggestions as to what I may do to try to narrow the problem down? It has 129,000 miles on it and 3/4 of them were open highway and interstate. It has a 4 cylinder engine in it.