911 Problem Need Advice.
 

Have an unusual problem with a 75 911. With the car engaged in gear when I decelerate the car will lunge back and forth. The engine and transmission have both been rebuilt recently and new tranmission and engine mounts installed. I don't feel alot of play in the cv joint axles. This almost feels like the car may be too lean (fuel/air mixture) and I have noticed that this problem isn't as bad when the car is cold, as it warms up it appears more. This problem is hard to describe but as I decelerate with the car in gear especially at lower speeds in the lower gears it will lunge back and forth, I can push in the clutch pedal and coast with the car in gear and it stops. Do I have a fuel injection problem (possibly a warped airbox) or fuel/air mixture problem or is this excess play in the transmission or axles/cv joints that causes the car to rock back and forth during deceleration. This is not a juddering problem when the clutch pedal is released. That problem was solved with a new flywheel. Any advice appreciated. Bill