90 Lumina 2.5 Bucking

[Mow38]

Im working on this car for a friend 90 Lumina 2.5 4cyl 140k.
The car starts and runs every time, never dies.
When you are driving along normally 40-55+mph the car will all of the sudden buck really hard about once every second or so, its very consistent. If you let off its stops, same if you give it gas.
I know the fuel filter has been replaced and that's really about it.
More or less hoping someone has dealt with this before and can help out quick. If not i know the drill haha If you need more info i can get it to you guys. Thanks!!

[Tech II]

Sounds like a basic misfire under a load....check plugs and wires, and do a coil output test......

[Mow38]

I got a little more info on what they have done. plugs and wires were on that list as well as a few other things the wife cant remember...so i'm waiting on that. For the miss tho it accelerates fine its more cruising. This is no slight miss tho...imagine the jerk you get when your trans shifts hard, that's the feeling you get..if that helps any

[Tech II]

This is probably a 3 speed automatic........

Chances are when you are cruising at a steady speed, say 50-55 up a slight grade, with the TCC engaged, the car starts to buck...you step on the gas and the TCC disengages and the car stops bucking......max load on the engine is when slightly accelerating while the TCC is engaged....

If plugs and wires were replaced, chances are you could have a bad coil(s)....that's why you have to do a spark output test of each coil.....