tbi engine chugging when going down the road

[lester622]

got a 89 chevy crew cab with the tbi 350, when you go down the road and even out at cruising speed it starts to chug like its advancing or retarding the timing to much/little. then when you turn it off sometimes when you go to start it back up its like the timing is way to advanced and it gives it a hard start.

i replaced the distributor module, unplugged the thing in front hte map sensor that controls the timing(forget what its called) and it still does the same thing. seemed to run better for a little bit but then started oding it again.

It just recently started doing this as of last week, and i have no idea what the problem is but i know gas milage has went way down and its killing me.

anybody have any ideas?