1985 380sl hard cold start followed by no warm start
 

1985 380sl with 200k+ miles does the following;

Cold, starts on first crank, idles @ 5 - 600rpm for a few seconds then stalls. It will re-start and immediately stall. Depressing the accelerator stalls the car right away. A few squirts of starter fluid allow it to start and run well enough to press the pedal to get the rpms up and keep it running. After 3 mins it will idle but it seems to constantly cycle between 600 and 630 or so and then fall to 350-400 every 10-12 seconds. If I bring the idle up to a steady 2000 it will still cycle between 1970 and 2040. I turned the car off and tried to restart after 10 mins. but it just cranks and cranks with no sign of starting. A few squirts of starter fluid made no difference at all.

If it is a fuel issue wouldn't the starter fluid at least fire her up for a split second?

what is the best way to check for spark?

If indeed I am not getting spark what would cause an intermittent spark failure?

The cap, rotor and wires are fairly recent and in good cond.

pull each plug out and while its out of the car plug the spark plug in the boot and touch it to the valve cover while someone is cranking the car, you should see spark.

Spark problems are a noticeable miss, not an "engine dies" situation. I would guess that you have a bad warm-up regulator. You are getting a puff from the cold start valve and fire, but then the control pressure is too high to keep it going.

There are lots of posts on this. Bottom line is that you need to check your cold control pressure with a gauge.

Chuck,
Thank you for your patience and expertise. Is there something like a engine/ignition control unit that prohibit any and all spark if it were to malfunction? I hae now waited 24 hours and it will not so much as hint at firing.

the rotor, or ignition control unit can stop spark.

thank you,
Is the ignition control the 2 plug box on the inside left fender towards the head lights? and will it fail intermittently?

Yes thats it. U dunno weather it will fail intermittently or not.

As mentioned, the coil, rotor, or ignition unit (or their wiring) can cause a total lack of spark. You can check easily by putting a timing light on a plug wire and see if it flashes while cranking.

Can you check if the fuel pump is running while cranking? Put your hand on it while someone cranks and see if it vibrates.

Generally the the iginition units either work or die completely.

check the green wire where it comes out of the distributor and then goes to the ignition unit.it carries a low level signal to the ignition unit and is the trigger.they tend to fall apart right where it exits the distrib and ground out causing no spark.the other common failure on those cars is the fuel pump accumulator[diaphram leaks] causing loss of fuel volume.