$0.02: sounds like 2 problems, yes the WRD if it runs much better cold then runs like crap with motor up to temp.
The pump is more like a cam and lifters: the cam pushes the lifter up compressing the gas. The lifter is called a piston. The piston can get stuck in the up position. do some seareching on the FIP in the tech manual. Afew people have explained with pictures, how to get the piston moving again.
Getting the FIP working right is a process: ignition in good shape, linkage adjusted, WRD working correctly, Warm idle. Those are the basics and foundation. Some go deeper and adjust the FIP. There are articles on all of this.
Most important: have fun with this great car.