i have no idea where to start with this problem so i guess ill start here. when driving down the road in overdrive or drive if i let off the gas to coast it sounds like the motor decides to fall on its face and the rpms drop. and then when you tap the gas it comes back and drives fine. let off again same thing. sometimes it surges and comes back by itself. i dont know where to start so i thought id start here. thanks in advance.
also has a code for the egr. could that cause this?

 

My car started doing some of the same things with surging and gas pedal hesitation. At times it sounded like I had a modified cam too. I suspected the EGR valve going bad. After a failed smog test with high nox pretty much confirmed a bad EGR (no code was shown in my case).

I changed out the EGR valve and found the new one from autozone to be defective (my luck I get the bad one in the batch). Replacement EGR valve worked and the cars runs great. Just my input. My or may not help you.

 

now ive noticed that it hesitates and stumbles before it winds up when i put it to the floor.