SD, the existing rear CPS must be functional or the engine wouldn't run. Based on your description it would be prudent to replace the other coil, both distributor caps, both distributor rotors, ignition wires and spark plugs with OEM parts. Those parts should make a dramatic difference in engine performance. Also, replace the fuel filter and both air filters.

For safety sake the owner needs to have the front end repaired too. The 140's are expensive cars to maintain properly. If your friend is in over his head then it would be best to sell the 140 and buy a more economical car.

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Fred Hoelzle