Un-even Idle
 

When we let off the throttle, the engine will dip in rpms, then go back to normal. What causes? Replacing the plugs might help a little, but i doubt that it will fix the problem.

This is normal for the 44. To correct you will need to chip the dme. I recommend the FRWilk chip.

Rick

There is a miss match between the mechanical idle by-pass on the throttle body, and the Idle Stabilizer.

At any thing above an idle the IS is closed. When you let off the throttle the engine RPM is falls faster than the IS can react to, so the engine "stumbles" coming to an idle.

The way to correct this is to put a jumper wire between terminals B and C on the service port located on the driver side fender near the brake booster, connect a tach to the coil primary (green) wire and ground, start the engine, and then use the by-pass screw on the throttle body to set the idle RPM to 840 +- 50 RPM.