Ive been having this on going issue with an error code p0440. Ive done some research as to what the issue can be and came across a large number of options. I was hoping if i give some examples of what is going on, maybe someone can help pin point the issue. Its a 2001 sls i have the service engine light on and the p0440 code. MY car will sometime while in idle begin to pulsate, the engine will wind up and down up and down. sometimes causing it to drop all the way down and shut down. Now i can turn the key and start it right back up but the problem will keep randomly happening. Now its at the point where it will happen while im driving! but only when i let go of the gas at around 25-40 mph the rpms seem to drop all the way down,pick up and then die. very sluggish feeling when it happens the car just kinda putters a bit. Ive replaced a fuel filter already just because i thought that was it so i cleared the codes and it came back. when its not pulsating at a stop sign or while in idle it runs fine, no issues with acceleration. Any help would be great

 

also forgot to mention i replaced an IAC

 

I bet its an o2 senser