My '91 Carat with manual transmission is running great with one exception. When driving in traffic and I take my foot off the accelerator but have the clutch engaged, the car bucks as if the engine is getting varying amounts of fuel.  A for instance is when I'm stopped at a light and want to creep up toward the car in front in anticipation of a light change, it bucks.  As soon as I give it a little gas, it smoothes out, no problem.

Any idea what causes this?  

Tom
'71 Westy, '85 Westy, '91 Carat