After several weeks of working fine I had a return of the problem. I've been making sure that the AC is off when I start the car, as that seemed to help when I was in the midst of tracking down the cause of the start/stall/start/chug-chug/run behavior. However, last week I forgot to leave it off and the problem returned. I was in a hurry, so I held the gas down, which made it start right up again, but it would stall as soon as I took my foot off. It even stalled a couple more times as I was coming to, a stop.

After that the idle seemed to drop down to a slower speed than usual, and it would cough and shudder a couple of times, though it didn't stall.

I decided to try my spare OVP again. I tried it when the problem was at its height but it made no change. Now that the other problems are cured, it did make a difference. It's been about a week since I put it in, and the problem has not happened again. Also, I've been starting it with the AC on to see if I can force it to fail. So far, so good.

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2000 Mercedes S500
1990 Mercedes 560SEL
1970 Triumph Spitfire

No return of the problem, but I decided a new fuel pump relay was in order and put one in. Now the car cranks about 1 second longer before it fires, but the revs never drop down as though it's going to stall after it does. They stay up there in the correct range for a warming engine, then slowly ease down until it's idling smoothly and at the right speed.

Of all the testing and changing of parts that I did, it seems the only ones that made a real difference are:

• New Injectors
• New (used) OVP
• New Fuel Pump relay
• New O2 Sensor

I'm glad I replaced the rest:

• Distributor Cap
• Rotor
• Ignition Wires
• Spark Plugs
• Crank Position Sensor
• Spark plugs
• Fuel pump
• Fuel filter
• Fuel accumulator
• Hoses leading to and from the ICV
• All fuses
• Air filter
• Coolant Temp Sensor
• Throttle Position Microswitch

As I now know what the state of the car's maintenance is.

Along the way I also aquired a spare EZL & ECU. Both tested and working fine.

It's been a long process, but the car is now boringly reliable. I just turn the key, put it in gear and drive away. At one point during my quest, fuel milage dropped to a little over 14 mpg now it's consistantly 19.5 to 22.2.

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2000 Mercedes S500
1990 Mercedes 560SEL
1970 Triumph Spitfire

replace coolant temperature sensor