95 seville engine/trans problem

95  Seville, 115,000 miles, northstar engine

When the engine is running and the transmission is in drive there is a slight bucking. If the trans is put in neutral the engine will run smoothly. This only happens when the car is at a standstill.

Any suggestions why this is happening will be appreciated. Thank you.

Need more info. ses light on or off .I suggest to check plugs,wires, and coil towers. If you see anything that looks like rust , that's where your problem lies.If it doesn't have AC plugs I would put in it.Hope it helps

Thanks for the reply. I'll check on the SES light and the other things. I'll be back as soon as I have more info.
 
Thank you again.