I just wanted to add for anyone experiencing this Throttle Delay behavior, that my ML55 was also experiencing this issue each day as I came to speed bump that would trigger it to occur. I've been hitting this bump for about 5 years every day, and the shock of hitting that speed bump at about 30-35mph must have over time caused the issue, as it began one day about 6 months ago. The throttle would start off normal after starting the engine, and then after hitting the speed bump, there was no increase response from the throttle for about 2-3 seconds. If you were to let off the throttle the response was normal and no delay was experienced. Needless to say, driving this way is quite the adventure.
After experiencing this and triggering the issue routinely, I began searching here in the Forums and ended up having a seeing the Accelerator Pedal sensor recommended being swapped out, so I had that installed and experienced no change. As luck would have it, I had the EGR replaced shortly after the last service, and after the EGR was replaced and I could not trigger the issue for 2-3 weeks. I thought the issue was sorted out but the delay came back. At the time of that service visit the Indy mentioned that I needed a new Gasket between the Air Intake tube and the Throttle Body. I went ahead and ordered a new Gasket and used TB from ebay in hopes that that would take care of the issue, as the TB was also suggested in a different thread, but after those were swapped in, no change was noticed.
Next up, was a thread mentioning to change the Engine and Transmission mounts. I had those inspected during the Transmission flush visit and decided to replace those as well, and after having those installed, no luck as well. This was turning into a classic case of throwing parts at the problem which I know is frowned upon, but my only Mechanic was not able to pinpoint the problem.
Back to digging in the Forum, the last suggestion I found in other Delayed Throttle threads was to change out the MAF, so what have I got to loose at this point? Luckily here in Korea, most of the shops will NOT charge you a single Won/Dollar if they don't fix a problem like this issue, even if they worked on the car for 3 days straight which they did. I love that that is how it works here, so up to this point I was only out the Pedal sensor, used Throttle Body and Mounts in Parts costs.
On to closing this saga out. The MAF was ordered and after being installed, and the problem was gone, no return of the Delayed Throttle in over 3 months. The ML55 seems to be a bit sharper now on throttle response, maybe 10% better response but I could be imagining things. Fuel mileage may have improved as well.
Also, every now and then I would get a idle stumble when just parked, were the engine would drop in revs for a split second and recover to normal revs 2-3 times in a 1 minute period of time. That odd idle is now gone and I don't know if swapping the TB fixed that or the MAF, but I think it was the MAF. I also had the voltage regulator replaced as the ML has 185k on it and the alternator is original, so don't know if it could have been electrical system related.
Hope this helps anyone experiencing this issue.