Great news: My car starts, runs, drives. Almost perfect. It still has some vibration at 1,700 rpm, but the engine is more powerful than ever since I owned the car.

I restricted the air to the MAF sensor with my hand on top, to see if system compensates by opening the throttle. It did not. I expected it to respond, but this may be normal. I don't know. After that, I disconnected the MAF sensor and things got much worse. The gas pedal became spongy and the engine unresponsive. I reconnected it. This part clearly works. Next, I disconnected and plugged all vacuum ports I could find. No change. Then, I listened to all 8 injectors. They all ticked. Finally, I noticed the car has no more symptoms. I don't know why, maybe reconnecting the MAF sensor helped, maybe the repeated restarting helped, but I drove it with the A/C on, and it flies.

I am yet to erase all codes and check for new ones. I will do a compression test, but may postpone it until I have to change the spark plugs again.

My wholehearted thanks to ALL who helped me sort through this! I could not have done this without your insight.

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2004 E500 4Matic 138,000 miles