After many months of replacing this and thinking it was that, I finally have my '91 300E starting like it was brand new ON THE FIRST TURN and catching on the initial crank like a NEWER car! Here is what I think has contributed to everyone's woes that I have repaired in mine:

1. Poor fuel pressure (Installed new fuel pumps, filter, accumulator and EHA Valve). Plenty of pressure the next morning and plenty of suction when removing that gas cap (was not like that before)

2. New Plug Wires and NGK Copper Plugs installed.

3. Flushed coolant and all the crud out. Put in Steel Seal ($80.00) with new coolant and ran in coolant per directions with heater on high for 60 min and let cool, etc.

4. Replaced all heater and radiator hoses and expansion tank as well as old thermostat that was corroded and stuck.

5. Installed proper 875 Amp Battery vs. the 610 Amp that PO had put in (what a spark and crank difference!!!)

6. Ran some more Liquid Head Gasket Sealant from BARS ($29.99 liquid stuff from Autozone that you can add to coolant and run for an hour with heater on high and then let cool overnight to seal any final cracks in block). This got rid of my smoke and the leaking coolant flooding into the cyclinders helping to create the hard starts! It works like promised and is still working and getting better by day.)

7. After installing new EHA valve I adjusted to correct duty cycle with Sears Duty Cycle Meter ($29.99).

8. Replaced o2 sensor prior to all of this and immedialtely noticed idle improvement.

9. Replaced coolant sensor on back of engine block and noticed even better idle back then.

10. Today, I replaced my thermostat which helps the engine get warmer faster during startup (upon examination my old one was all corroded and spring was jacked up for some reason) unlike my old one which remained stuck and kept the engine cool too long (engines like 90-95 degrees celcius temps to run smooth).

11. Replaced Cold Start injector with one from "Used-Bay" for $35.00. Don't know if it changed anything but now, freezing cold, warm, or sweltering, same start and idle, and temps (92-95 degrees).

12. Replaced Fuel Injectors for $25.00 a piece. Easy to do.

What questions do you have?

Happy Guy...for now