My SD will skip and run rough after its started. In my case after eliminating a few things I think its either a weak injector or a weak cylinder.

It could be air leaking into the system as well. If you have covered the basics like making sure the valves are adjusted I'd pull the injectors and have them tested.

Also if you have the old style hand primer pump you may have an airleak, switch to the updated one.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200