2000 Nissan Altima Rough and vibrating Idle with low rumbli

Is the check engine light on? First thing you need to do is have the codes read, Autozone does it free, Post the results with the code number(s). Even if the service engine light is not on, there should be freeze frame data stored.
If it won't make it to Autozone, buy a cheap scanner, they can be had for 30-40 dollars, a good investment, since they cover all cars sold in the USA from 96 on...
If the light is blinking, it means possible damage to the converter...service it right away!
It is probably time for a complete tune up, plugs wires and all filters...then go from there.

I will take it in to have the codes read today, thanks. It does drive, but I am afraid of breaking down, new to the area...husband away...don't know too many people...20 miles out of the nearest town, a little nervous to drive it.

Also, the check engine light is NOT on. Six months ago it was on, after reading the owner's manual, it stated it was most likely an emission control issue that if the light didn't turn off after a few driving trips to take it in to have it serviced. It did in fact turn itself off, so I didn't take it in. It has not come back on since.

Thanks again, I'll post the codes.

but there were no codes. The guy that ran the test, said that maybe I had a broken motor mount? He said they were hydrolic motor mounts.

When I left the house I had to get gas because I was almost out. I had put a few gallons the other day in it, but I only put in 85 usually I put in supreme. When I left the gas station it got 10 times better...? When I start it now, it starts at a hi rev, then kicks down to a regular idle. same thing at stop lights etc...But whe I am driving, it is is not nearly as bad, but i do still HEAR vibration, I don't ffel it, I hear it that same rumbling sound.

Could it have been bad gas? that could explain the overnight poor running I would suppose.

I am still going to take it in this week for a tune up.

But do you have any ideas? Bad gas, bad motor mount? Now I'm more confused! Gald it is running better...Thanks again for your assistance.
Lynne

Even tho were are paying 4:00 dollars a gallon, some jerks still add water! It is possible...good luck with it, when you go for the tune up, would'nt hurt to have the mounts looked at too!

Thanks!!