Just fixed my idle problem today. Does Your engine shakes because the idle in drive or reverse is too low? My car would idle at 600 to 550 in drive and the car would shake really bad. To fix this I had to set my idle from the ecu by turning the screw to the desired idle. Move the screw clockwise a little and then put the car in drive or reverse to see where your idle is at if its too low move it somemore and if too high move it counterclockwise. Now this fixed my 97 maxima se and in park the car idles at 650 and drive 650. No more shaking. The car feels like it not even on at all. Before this fix I had changed all my coils, maf, and all of my sensors to fix this but nothing worked until this. I will put a video on YouTube showing you how to do it. Heres the video link

 

So what you're saying is you adjusted the idle screw to adjust the idle?

Check your motor mounts. Changing the idle speed via the IACV is a band-aid. My 99SE idles perfectly fine at 450-550rpm in D or R when warmed up, no issues.

 

Not the iacv screw, the ecu screw. The iacv wouldn't do anything but besides raise the idle in park or neutral but when I would put it back in gear the idle would be back at 550 and the engine would shake really bad. All the motor mounts were good and all the sensor and coils were good as well. I even tried new fuel injectors which were bad but still had the same problem also tried fuel pumps nothing worked besides this.