Sounds just like the V70 I had. Multiple mechanics were familiar with the problem and all told me it's the throttle controller Volvo used for a few to several years around the time your car was designed and built. They said a new one costs several hundred to more than $1,000, and that in theory you could find a used one and try to install the software or find someone who could do it for you. Each recommended junking the car, which at that point was worth less than the part -- if it ran. Each mechanic, even those specializing in old Volvos and normally fond of the brand, spoke quite harshly about Volvo's decision to use this part. I wish I could offer more hope, but I got rid of the car for $400 and will never buy a Volvo again. Perhaps you're lucky and it's something else, but it doesn't sound good. Good luck.