I have a new E320 4matic wagon (600 Miles) which has developed a low speed throttle lag. Driving in a parking lot at 2-3 mph, apply a little throttle and nothing happens. Sometimes it acts like it's going just stop running. My dealer tells me to switch to regular grade (87 Octane) fuel. Is he right, or just trying to avoid a repair? Problem shows up more it wet driving conditions. I've added 8 gallons of 87 to tank which had 92 in it. After a short 7 mile drive it seemed to be better. Is the vehicle equiped with a fly-by-wire throttle system that might need a sender unit or servo motor replaced?

87 for a new E320? And that too from a dealer? Get it from him in writing, and then sue him. For a long time, all mercedes engines are designed to run on 91 octane or more.

Never use regular octane fuel in any MB after 1987!
Yes the system uses throttle by wire.
Have someone in service dept ride with you in their parking lot, if you can get the problem to happen all of the time.

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I have a 2000 E320 with the same issue, you will have to get used to it and it won't bother you. I also had an ML320 and it had the same problem. You'll adjust....