1995 Chevy Corsica car bucks at speed

The car idles fine, accellerates without any problems then when at speed it begins to buck. Over sixty mph it seems to clear then the check engine lite comes on. While the lite is on the car seems to run fine even when slowing as long as the lite is lit. Then at a stoplight the check eng lite will go off and the car will do the same as before, it begins to buck as before then somewhere between 55 and 65 it clears and the check engine lite comes back on. It runs fine till you slow enough or stop then the check eng lite goes off and it repeats. Any ideas?
tnx for ur time

Bob