Starting issues
 

Perpetrator is a '99 E320. The engine will sometimes start and immediately die, as though it is not making the transition from start to run mode. It will usually start properly on the second or third try. I suspect a faulty relay somewhere. Already tried the fuel pump relay, with no luck. Any suggestions?

Thanks, Rick

Responses?
 

Won't anyone admit to knowing how the W210 starting circuit operates?

Surely someone here does, please help!

I would start by scanning the OBD to see if there are any pending codes. The ECU checks for a number of conditions and shuts down if it's not happy. If no codes, I'd check fuel pressure and exhaust system back pressure. Also, the throttle position sensor.

One other area to look at if you do a lot of short trip driving is the EGR circuit. Check the oil filler cap to see if any sludge is building up on the under side which is a telltale sign. If so, the lines from the EGR valve to the valve covers may be plugged.

It's most likely throwing a code. Start scanning and give us the code.

The crankshaft position sensor is a frequent culprit in hard starting issues on the M112/113, but I think the symptoms are usually worse when the engine is warm.