It took me a year to solve the same problem with our 124 260E. We did all I thought was right according to the manual, from changing of plugs to tuning but nothing worked till I decided to replace all its injectors.

We had 6 injectors replaced, along with its plugs. That made a fair bit of difference.

The biggest difference to cap of that improvement was replacing a new accelerator cable. Made the acceleration light and the power resumed to normal.

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... Kerry

126 tailed by a 203, 129 leading the pack.