I was driving home from friends the other night and all of the sudden cruising at about 55 mph truck just suddenly decided to accelerate for just a couple of seconds. Then it went right back to normal. Did this twice on the way home. Ran my codes from memory and got 18 loss of ignition, 33 EGR Valve closed or erratic, 67 Clutch switch failure. Also got KOEO code 85 canister purge circuit failure. Does anybody know which of the codes might be the cause? Also any help with the other codes would be great I'm trying to get truck all ironed out for camping season which starts right about now. Truck is 1991 F150 4X4 351W
E4OD.