Problem Trans C4 automatic

This?

Not likely. The vacuum modulator that is pictured controls shift points when you are driving. It does that based on the amount of engine vacuum. If the vehicle jerks when shifting out of park (P) into reverse (R) or drive (D) your idle speed is most likely too high. Idle speed should be adjusted with the transmission in drive (D), parking brake set, high beam headlights on, air conditioning off, and the vacuum advance hose at the distributor disconnected and plugged. If you have air conditioning set the idle speed at 650 RPMs. If you do not have air conditioning set the idle speed at 600 RPMs. Hope that helps! Jim

Thanks a lot for the answer. The problem makes me a car in "Park" - “drive” when I insert "Drive" or "Retry" I feel a “stoc” ... then it moves. problem the modular vacuum?