A question about the engine
 

With light throttle, just off idle, my engine surges. Always when cold. I don't have an audio, but it's like "RRR-RRR-RRR" The engine is otherwise just fine. No hesitation, and it kicks me in the pants when I blip the throttle while at normal speed.
Not having had the car for long, I wonder if this is normal for this 2.5 base.

Comments?

TIA

I get it sometimes too in my 2003 S. When the engine was completely stock it would happen every once in a while. Now that my engine has been rebuilt as a 3.6 with LN Nickies, Fabspeed Sport Headers and a Softronic custom tune I am getting it more often. It seems to happen when the engine is cold or not fully warmed up and at small throttle inputs after shifting from first to second gear, and sometimes also from a standing start in first gear, like at a red light after it turns green. The experience from standstill can be much more of a herky jerky surge. Next Tuesday my car will go on the dyno at the shop that did my rebuild. The tune will be verified and it may be tweaked by Softronic if necessary. They will drive the car when it is cold first thing in the morning before putting it on the dyno. I am hoping that it will happen for them as it doesn't happen all the time.

And I will get to watch and have a printout of my HP and Torque curves when all is said and done!

I've owned my 98 for about 3.5 years now and I would say it's normal. Seems obvious but check if your air filter is dirty. If really dirty the car does what you are describing. When my car it up to normal operating temp if purs when idle with no shaking.