Hello and good evening. Look for the vacuum line that comes from the firewall for the air conditioning. That vacuum line is either cracked or the vacuum line that goes to the vacuum reserve canister has become disconnected. When you accelerate, vacuum diminishes normally, that vacuum canister stores a reserve of vacuum to maintain vacuum during those times. You most likely disturbed one of the vacuum lines replacing the plenum. The lines from the air conditioning is usually a small black hard plastic line and the one going to the vacuum canister is most likely rubber. Let me know if you need anything as you proceed through this.

Your JA Expert,

Ivan

Ok, I'm going to start with these 2 diagrams. The first shows the vacuum feed to the HVAC system. This line will come right off the upper intake manifold and go into the firewall as a black hard small plastic line. Look for that item and make sure the line is not damaged anywhere. The second picture is the location of the vacuum reservoir. This is located under the vehicle. The instructions tell you to turn the front wheels to the right. It will be mounted forward of one of the front wheels. This is what is responsible for keeping vacuum under low vacuum conditions. With the car running, unplug the vacuum line to it and see if you have good strong vacuum at it. If you do not, you need to look for where this line became cracked or disconnected from the intake manifold. That will be the reason. Come back to me if you have any questions. You should have full manifold vacuum at that vacuum tank. I'm having trouble uploading the pictures. Look for my next post for the 2 pictures. I'm sending them right now.Ivan41090.9975285069