Engine idles errratically, and when accelerating it will not pick up speed until kickdown comes in. Took it to shop and fuel injectors was replaced alone with regulator. I've had a tune-up with new plugs, fuel filter, air filter, new cap and rotor. I have notice that the backing plate under the dist. cap and rotor has burn holes in it as if it has been arching. could this be the problem?

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Do a search on the topic!!!!! What year is your car? How many miles? What about the cables and coil? Did you jumped your car recently? If you did, I would check the overvoltage relay fuse. It is located behind the batttery, it a silver cylindrical box with a red plastic cover/top, it has an "american" type fuse. Are you sure the cap and rotor were replaced?
Start with these simple things, and go from there...
Good luck!!!!!

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J.H.
'86 300E

I had a similar promlem with unstable idle on my 300CE and the problem was the idle microswitch.
Remove the air cleaner completely, top and bottom to reveal the throttle linkage. Make sure all the linkage and the switch are clean , mine was covered in oily dirt , then check that the microswitch clicks every time the gas pedal is up.
You may need to bend the switch arm very slightly to make it work every time
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Larry

I had a similar problem with my 1988 300E, and was solved by cleaning the temperature sensor contacts. Hope this helps.