Quite a nightmare ........ If you really did put sugar in your tank as your "mechanic" suggested the fuel filter is probably now plugged up. There's an old story that sugar in the tank would ruin an engine but I've also read that it doesn't dissolve in gas so hopefully your filter got it all. Looks like you're looking at spending a few more dollars but find someone who is a honest capable car mechanic preferably one that knows Volvos. Don't take it back to this guy !!!! You don't deserve this sort of abuse. Check all of the electrical plugs in the engine compartment. He's so incompetant that he may have only partially plugged in some connector and it fell out.