Difficulty starting

[CraigTPE]

If the car sits for several days, it starts fine. If the engine is off for just a few minutes, it also starts fine. It has problems starting, however, if the engine is off for a couple hours. This problem happened before. The dealer said that the plugs were fouled due to a rich fuel mixture, which was set to resolve a rough idle. After cleaning the plugs, the engine started easily in every situation. This time, however, they claimed to have checked the plugs and nothing was wrong, but the starting problem remains. The service manager is speculating that it could be a problem with fuel pressure and I should take it in. I am skeptical. Any thoughts?

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[Richard / E320]

Originally Posted by CraigTPE

If the car sits for several days, it starts fine. If the engine is off for just a few minutes, it also starts fine. It has problems starting, however, if the engine is off for a couple hours.

While I understand that your specific problem is not exactly what I experienced with the 1987 420SEL that I previously owned and absolutely loved, with less than 70k miles on it, it can show you that a seemingly straight-forward issue is not so easy to remedy. Unfortunately, my vehicle developed what I call a cold-start problem. After sitting for some time, it would start and idle no problem but then upon driving it a block or so, it would choke up, or load up for just a moment upon acceleration, usually at take-off from a stop sign or stop light. A few times it felt like it just died (but the motor never actually quit) and I was going to be a sitting duck for the cross traffic.

I had all the vacuum lines replaced, along with all the rubber tubing that had anything to due with air intake or fuel, new spark plugs, new fuel injectors and seals. I also replaced items like a couple of cold start valves and idle value (don't remember the exact names of the actual parts) but three valves or solenoids. It had great fuel pressure but the next thing the indy shop wanted to try was the fuel injection head. If they could have assured me that would have solved the problem, I would have done it, but the shop couldn't make that promise and after spending $1,800 trying to chase down the problem, I gave up.

I sure miss that SEL though, and have always wished I could have sorted out the problem.

EDIT: Poked around some of my old threads here and the other M-B forum, and found the more correct names of the following parts I had replaced trying to get the issue resolved.

Part #0065454524
Behr Thermot-Tronik
Engine Temperature Sensor; 105/115 Degree C with Green Insulator and 3 Pin Connector

Part #0280130044
Bosch
Engine Temperature Sensor; 2 Pole Green

Part # 0001411625
VDO-Siemens
Idle Air/Speed Control Valve