1999 V70 wagon, compression went to 30% in one cylinder, mechanic saying options are a used engine or $2000 repair.

What will happen if I keep driving it?

At idle engine bounces around a bit, but on highway I can't tell the difference, sounds fine, and seems to have all the power it ever has.

Thanks for replies.

 

Most common would be a burnt valve - you can keep driving but it may be running on 4 cyl very soon. It will just idle rough - perhaps be hard to start.

Be on the lookout for your next car>