I just wanted to say thank you andy_george for this old post! I mysteriously had the same problem with the engine surging and hesitating while accelerating. I changed my taillight bulbs to LED but I didn't drive the van for about a week after I changed them so I didn't connect it as the cause. Never in my wildest imagination would I have suspected the LED taillight bulb to cause such erratic engine behavior! What was strange in my case was after about 10 minutes of driving/warming up, the problem would slowly go away. If you let engine cool off and start driving again and the surging would come right back!
Thank you again, this post certainly saved me hours maybe days of diagnostic time/parts and probably dealer labor after I probably would have given up!
