I know a guy who is trying to sell his 91 190E, but it has this starting problem and it makes me very apprehensive to think that if I buy this thing it may be impossible to start the next day. He says it's that idle mixture adjustment screw (which is adjusted through the top of the air cleaner), but I suspect a fuel pump.

Here's what's happening: He takes his screw driver and tweeks the screw, then cranks on it for a few seconds. It doesn't start. He then goes back and adjusts the screw slightly, claiming he's trying to find that position where the car will start. This process repeats for about 5 minutes until the car finally starts and seems to run just fine. It can be restarted quickly and idles at the correct speed. He claims that he can't get the screw quite right because it requires a special flowmeter that only a dealer has.

I think it's just a fuel pump or fuel distributor and all that cranking allows it to eventually build up enough pressure to start running and that it would start regardless of the slight tweeks to that screw. Yes, changing the idle mixture adjustment will alter emissions and the way the car idles, but it won't really keep it from starting will it? And once he gets that screw "right", it should continue starting without going through that every morning, correct?

If I had more confidence about what the problem is I might go for a pretty good deal on this car. Anybody agree with me? How tough is diagnosing/replacing a fuel pump problem?

Hard cold start could be number of things but a failed fuel pump relay (not actual pump) is near top of list. Can you hear the relay activate the pump when the igniton is turned to position 2? Its a pretty loud hissing sound and comes from near LHD drivers side rear wheel. The pump will hiss away after the start up if its dying.

Mike.

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1990 Euro 190e 2.0l Petrol Now Sold Maybe a w116 280se next

You are right on the money when you suspect a fuel problem, but the culprit is most likely leakdown, often caused by a defective one-way valve on the fuel pump discharge side (although it can also be caused by the pressure accumulator, leaky injectors, leaky fuel distributor, or a bad pump, which will "stick and catch" when first engaged, until it has run for a short time). I don't know where this guy that's selling the car got his info from, but the only reason the CO adjustment might be a culprit is because he's screwed it up in the first place. If you want to mess with him, tell him it's the ignition assembly, then start it up on the first try by cycling the key to the "on" position 3-5X to cycle the fuel pump; if it doesn't start the first time, look at the fuel pump or relay. One-way valve is ~$30, but you will need a pressure gauge set to examine the residual pressures; the fuel damper/accumulator would be a good idea to replace as well.

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