93 Nissan Maxima with 150000 miles.

I’m experiencing a problem of vibration during very low speeds and at
rest. I don’t know where the vibration is coming from. But at rest I
noticed my exhaust going puff puff at a greater interval than a car
without a vibration might have.

When I turn the ignition on, the car seems perfectly normal from the
outside.  Even with my hood open, I see no visual or audio problems
coming from the engine.  But as soon I get in the car, I immediatley
noitce vibration on my steering wheel.  When I accerlate, again the
steering wheel vibrates a bit with a small noise I haven’t heard
before, until I reach about the speed of 30 MPH. After 30 MPH the car
seems to run fine until I break and stop.

I am a bit worried, cause the symptoms are similar to my oldsmobile I
had when I was young.  In the oldsmobile case, the symptoms got worst
and eventually led to constant engine shut off.

The symptom just started today.
I want to get some of your opinions before I take it in for service.

Someone told me if I am lucky it could be just a minor problem that
can be fixed by changing such things as the spark plugs.  That could
make sense, since it’s been 40, 000 miles since I had a tune up.

Help