I attmpting to diagnose the P0455 code problem on my '97 E320. I have replaced the gas cap but keep having to clear the code. I was examining the purge valve operation and have the following questions:

1) When does it operate?
2) Does it always pass the same vacuum strength to the components at the tank?

When I first checked mine, it was not operating. Drove the car and got it hot. I could then hear/feel the valve pulsating. I pulled off the hose leading to the rear of the car and the vacuum thru the valve seemed very weak. I jostled the valve a bit and then got a much stronger vacuum level.

Any explanation for why CEL usually pops on at a long idle, e.g. traffic signal, after a drive at highway speeds? What would be the consequences of putting a shot ow WD40 in the tank side of the valve?

TIA to responders.