Could this be motor mounts?

Check the ohm resistance of each ignition wire.

How many miles / kms on these spark plugs?

Have you added fuel injector to the fuel?

If the spark plugs are relatively new, the ignition wires OK and you're satisfied that the fuel injectors are clean then its time to seriously consider the motor mounts.

Yeah... I would say age gotten to the engine mounts.

Hi TG: Spark plugs, wires, dist cap, rotor, all new (two months, Beru). I'm certainly not completely satisfied about the injectors (slightly difficult warm start). I've tried to clean them with several different brands of cleaners in the tank. The following step would be ultrasonic cleaning, but where I live new injectors does not cost much more. So, from yours and Tiger´s answers I'm now thinking that both engine supports and injectors are old enough to get replaced. Thank you. MMansilla

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Hard warm start is usually the fuel accumulator.

Well, Yes. I posted my warm start problem here a while ago and was adviced to check the accumulator. I then disconnected the rubber hose between acc and fuel line, and it wasn´t leaking any fuel. Someone else told me to change the fuel filter, it was almost new, but the car had been sitted several weeks while on sale before I bought it. I changed the filter and the hard starting improves let's say 60%. Interestingly the fuel coming out from the back of the replaced filter was cloudy, full of sediment. Maybe this is normal for a filter doing its task (yes, that was my first fuel filter replacement job), but anyway, still the warm start difficulty remains a little, so I'm suspecting a leaking injector due to somehow similar reason, wich on the other hand could be affecting the idle. Regards, MMansilla.

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Sediment is not normal... meaning someone dumped sand into fuel tank.

No, sorry, ...I didn´t meant it in that way. There was not visible solid particles in the filter's fuel. Just it was not translucent. I´m theorizing that while the car was parked for a long time, a thin layer of fuel impurities (or tank rust) was deposited at the bottom of the tank. When the car started running again this layer went right to the fuel lines, this way clogging the (almost new) fuel filter and prehaps other fuel line points.

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Oh... okay... then yeah, it might be totally possible the new filter is clogged.

Well, it was.

I just installed the engine right, left, and transmission mounts. Total parts US$180 at local MB dealer, and easy DIY job (on the lift). The effects of changing them went far beyond the idle. The car is accelerating and breaking much better now, suspension improves too. The whole running is more "solid" and smooth. The old engine mounts were apparently in good shape, but they were 5 mm smaller in height than the new ones. As for the idle, it improves but the seats still shake a little, symptom of a not even fuel injection pattern, I think. So, next job is injectors. Thanks for your help. MMansilla

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