300CE weird behavior

My 300CE seems to be having some weird issue lately. Heres a quick run down of the story:

It seems after a trip driving from the SF Bay Area down to LA and back, the car would smoke at the rear of the engine. It still continues to do so. It smells like oil but my oil level has not dropped in over 2 weeks of it smoking. I've checked pretty much every day.

But something else has arrived now. As of yesterday, I was driving down a normal route I go and stop at a stop sign. Suddenly I get vibrations and the engine starts to idle rough. I accelerate and it feels like ABS brakes are on as I get the kinda quick continous thumping feel but ABS is not on nor the brakes. So I was careful with accelerating and barely touched pedal. I noticed if gave it a little more gas, I would get this popping sound. After 2000rpm seems to be somewhat smooth. This whole issue (except for the smoking) seems to be erratic as I'll be driving with this problem and then it disappears and will re-appear at some other time. When its not having this problem, the engine runs perfectly fine and no popping sound, even when I floor it.

Anyone have an idea? Tranny issue?

Thanks