W126 "Strange" acceleration
 

This isn't a problem really. The car starts and runs OK, with slight roughness at idle. Its just that when picking up speed at more than half throttle, there is a noticable stepping effect, like the engine gathers speed, pauses a moment, and then continues accelerating. It happens in 2-3 second cycles and is not related to gear shifts. Its usually very mild, and not noticable when driving in 'economy' mode, so I'm wondering if anyone else has this. I'm guessing its fuel system/ECU related?

Had a similar issue on my w126. Turned out to be a burned rotor and cracked distributor cap. Easily checked, but be careful not to loose track of the proper alignment of the cap and don't pull the spark plug or coil wires off! Just pull off the plastic cover on the very front of the cylinder head to expose the distributor cap. (releases with friction clips on both sides.) Then find the three allen screws that hold the distributor cap in place and remove them. Once removed look for signs of charring and cracking under the cap. If just dirty clean with a rag, if cracked replace the cap. You can clean up the contacts with fine emory cloth or sand paper. The rotor is now also visible and should have a smooth appearance on the pointed end. Sometimes cleaning this up with emory cloth or fine grade sandpaper will work. Otherwise you may have to replace. If this all checks out and problem continues, you may need to scope the car to look at some of the relays, etc.

Thanks. I will check that. State inspection also found a bad engine mount, and I'm thinking maybe if the engine is rocking excessively, that could be changing the throttle position while driving. After doing those 2 things, I'm not inclined to look too much more into it, since its more of a minor nuisance than a real problem.