Someone advise me!
My 99 volvo S70 has 194,000 miles on it.
We had to replace the electronic throttle piece a couple of years ago (at a very high cost!).

Today, my car started up fine. About 10 minutes into my drive home, I noticed it was running a little rough at low speeds (under 15 mph). When I got home and parked it, it was idling terribly, very rough. Almost like it was going to stall out, but it didn't.

I checked the oil, it's fine.
So I left it alone for a while and went back, cranked --- still the same terrible idle, and now my "Check Engine" light is on.

What could it be?

 

Have the codes pulled.
Then let us know what they are.

 

Does the dealership need to do that? And how much does it cost?

 

no autozone should be able to pull the codes for you. check and see.