Just under 85K miles on car. A couple of nights ago I suddenly lost power and acceleration. Dash said "reduced engine performance". I pulled over, shut engine off and started it again. Light was off, and everything appeared back to normal - temporarily. Problem reappeared almost immediately. Found air intake hose loose both top and bottom. Looked like it was damaged at last oil change. Crack in it on the bottom. Temporarily fixed by applying duct tape, and reattaching hose securely. Performance immediately improved greatly; more responsive at slightest tap of accelerator, and light was again out. It ran great for the next 15 miles, then suddenly the same problem reappeared. It has the "feel" of a dirty fuel filter, but I don't understand how that could cause such a sudden change...? Help please! The car is no longer under warranty and I cannot afford a huge dealer bill, chasing what appears to be a very illusive problem.
Reduced engine performance on 2005 Volvo S40
You really need to find a good Volvo specialty shop with a DICE diagnostic computer to see what's causing the problem. This is the only way to fix it properly, otherwise you will pay for a guess, which might just waste your money. The cheapest way is usually the right way.