Re: Volvo Penta 3.0 that hasnt been used in 2 years...
I highly recommend it to be serviced by a Volvo dealer. Preferably someone that has been in the business a long time. I can speak on behalf of my forty years of servicing Volvos. The $600 figure seems very high. My shop is about half that amount. You need to change all fluids, engine oil, filters, both oil and water and outdrive oil. Tune engine. Replace plug. Have an expert clean and repair carb. It has a two barrel holley. Your rough running is the economize valve in carb. Install a new Holley kit. Just a good tune up. You can buy a genuine Holley kit at most automotive parts dealers. This kit is found in the high performance section of Holley parts. Adjust engine to specs. If you have a question you can call me at 1-800-949-2189. Good luck.