I have a 2003 Silverado with the 4.8 engine with 63,000 miles. Since I purchased truck in March 2010, I have been getting a 'Reduced Engine Power" message and have to pull over and restart. I pulled code last night and got a P1518 (intake manifold runner control valve fault stuck open) any suggestions?
I don't know where you got that definition from but it doesn't apply to your vehicle. The definition on yours is. "Throttle Actuator Control Module serial data circuit"
Your truck has a "drive by wire" system with all electronic throttle controls and there is a problem with communication in the system. This is not going to be a DIY type job as it will require some special equipment to diagnose it properly.
Check to see if your battery is any good as well as your grounds. That is one of the things that will set this off. As you have a 2003 and its 'the original battery it's on borrowed time. But also make sure your charging system is up to snuff as well. That is your lTAC module that is givin g you troble or throttle actuator control module.