1. Electronic Throttle Module
If there is intermittent engine idling or sudden "Limp Home Mode" driving, the Electronic Throttle Module (ETM), which keeps the speed of the vehicle and engine idle as well as the cruise control in check, may be acting up. A "Check Engine" or "ETS" warning message, however, should best single out the problem at hand. To avoid compromising one's safety on the road, any of these solutions should be considered: (1) cleaning and refitting of the ETM, (2) replacement of the ETM, and (3) software upgrade for the Electronic Throttle System.
Several years of routing electrical current to components like headlights, power windows, fuel pumps, cooling fans, Anti-lock Braking Systems, ignition circuits, air con compressor clutches among others eventually take their toll on the relays. Once this happens, these components would naturally stop operating. Though it may seem that the culprit is solely a blown fuse, investigation of the problem should not stop there. Replacing the fuse could prove to be just a temporary fix and may indicate more serious electrical problems. Thus, bypassing the relay to see if the related component could still be restored is necessary. In doing so, too, a rather costly misdiagnosis of the problem-buying a new fuel pump when it is just the fuel pump relay that needs a replacement-could be prevented. To accurately check the relay's condition, a scan tool or an ohmmeter may be used. Once the relay has been identified as broken, a replacement is essential. The relay with the correct part should be installed to avoid premature failure and further damage.
2. Fuel Pumps
In some front wheel-drive vehicles, there appears to be a problem with the right rear shock upper mount being unable to deliver the shock throughout the body. This then cuts off the fuel pump connections, leading to the wire harness short circuit and a likely wire thawing. The easy solution to this is to replace the fuel pump to restore the efficiency of the fuel system. To complete the fuel pump replacement, the fuel filter should be replaced as well because it might have been contaminated with metal particles from the damaged fuel pump. A faulty fuel filter won't do you or your Volvo any good so better to replace than repair and regret it later.
4. Air Idle Control Valve
Experiencing rough idle from time to time or simply being unable to idle if the vehicle starts at all could mean the Air Idle Control Valve (AIC) is defective. The AIC, which is part of the intake system, allows air to pass through the throttle body to ensure that engine idle is smooth. So if you're getting some rough idling, chances are, it's due to an AIC-related problem. Usually, cleaning the valve with a carburetor cleaner and a screwdriver set, making sure to take the sludge off it, can easily fix the problem. If nothing has changed, though, the AIC should be better off replaced with a new unit.