No offense to diesel cars or their owners intended...

My 1987 260E has had a problem starting for a long time - as in years. It has progressively gotten worse. It used to be just cold starts, but it is now every start. It is a beautiful car with the exception of this nasty problem.

I am so tired of passengers asking if my car is a diesel!

On starting, it first fires on just one or two cylinders, then a couple more, then all six. If it is not revved, it would simply shake and rattle for 10 or 15 seconds before it smoothed out. Once revved, it clears up, but occasionally gives up a faint puff of gray exhaust smoke. It's occasionally black, but that may reflect an annoyed HARD rev of the throttle tossing some carbon out.

I have heard that it could be all kinds of things. I remember a similar problem in a 1980 VW Rabbit I had in college. I changed the fuel line check valve in that car and that solved it.

I therefore tried changing one of the two fuel line check valves in the Benz, but perhaps I guessed the wrong one, (I had a 50/50 shot) or this wasn't the problem. No change.

I checked the plugs, rotor and cap. All good. I must guess that is most certainly a fuel injection problem, not an ignition issue.

What tests can/should I perform?

Appreciate all thoughts and/or uneducated guesses.

Check the fuel pressure first,cold start valve,you can try turn your ignition on & off five or six more time before you start your vehicle(this way fuel pump will pump 1~2 sec each time ignition is on)if vehicle start fine then you have problem keeping fuel pressure in your fuel system.

My dad's 260E is one heck of a starter. I've always wondered why the 260s were hard to start as I found it to be a common symptom for most 260E owners.

The answer may lie with constant check on the plugs - as these creatures are highly sensitive to the plugs. Wrong plugs used, or dirty plugs may cause it to be cranky.

Next on the line - as you guessed right, are the fuel injectors.

For my dad's 260 - I had the injectors taken out and cleaned one by one. Put them on again, adjusted the CO for that smooth idling - and hey, the starting improved tremendously.

Okay, it still plays up once in a while. But its much much better.

The idling is another matter. I recommend changing the idle control valve.

i have the same problem with my 190e2.6, and the problem manifests only when the engine is hot and ambient temp is not cold (i.e., spring or summer - no problem in winter, thanks).

no problem starting, but have very rough idling up to about 2000rpm, and i have to let the engine "clear its throat" before moving out.

once on the move, even during idling in traffic, the problem does not resurface. Seems like a fuel delivery problem to me at hot startup, like the pump or reservoir not being primed, or being vapor-locked due to the heat.

OVP relay is bad